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 $216.97   7.628%   $233.5205   $233.52   $233.50   $233.50  
  Purchase #2 $113.46   3.834%   $117.8101   $117.81   $117.80   $117.80  
  Purchase #3 $224.61   8.610%   $243.9489   $243.95   $243.95   $243.90  
  Purchase #4 $201.74   11.240%   $224.4156   $224.42   $224.40   $224.40  
  Purchase #5 $38.60   6.577%   $41.1387   $41.14   $41.15   $41.10  
  Purchase #6 $139.40   13.353%   $158.0141   $158.01   $158.00   $158.00  
  Purchase #7 $239.56   4.825%   $251.1188   $251.12   $251.10   $251.10  
  7 purchase totals = $1,174.34       $1,269.9667   $1,269.97   $1,269.90   $1,269.80