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 $227.97   3.261%   $235.4041   $235.40   $235.40   $235.40  
  Purchase #2 $61.27   7.211%   $65.6882   $65.69   $65.70   $65.70  
  Purchase #3 $174.29   3.388%   $180.1949   $180.19   $180.20   $180.20  
  Purchase #4 $239.42   5.524%   $252.6456   $252.65   $252.65   $252.60  
  Purchase #5 $37.62   4.810%   $39.4295   $39.43   $39.45   $39.40  
  Purchase #6 $34.28   3.518%   $35.486   $35.49   $35.50   $35.50  
  Purchase #7 $180.46   12.179%   $202.4382   $202.44   $202.45   $202.40  
  7 purchase totals = $955.31       $1,011.2865   $1,011.29   $1,011.35   $1,011.20