Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $213.49   5.397%   $225.0121   $225.01   $225.00   $225.00  
  Purchase #2 $225.84   13.624%   $256.6084   $256.61   $256.60   $256.60  
  Purchase #3 $153.32   11.396%   $170.7923   $170.79   $170.80   $170.80  
  Purchase #4 $166.86   10.109%   $183.7279   $183.73   $183.75   $183.70  
  Purchase #5 $64.26   4.711%   $67.2873   $67.29   $67.30   $67.30  
  Purchase #6 $243.52   3.267%   $251.4758   $251.48   $251.50   $251.50  
  Purchase #7 $210.88   13.860%   $240.108   $240.11   $240.10   $240.10  
  7 purchase totals = $1,278.17       $1,395.0118   $1,395.02   $1,395.05   $1,395.00