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 $213.90   12.742%   $241.1551   $241.16   $241.15   $241.20  
  Purchase #2 $164.93   5.387%   $173.8148   $173.81   $173.80   $173.80  
  Purchase #3 $138.57   3.203%   $143.0084   $143.01   $143.00   $143.00  
  Purchase #4 $86.97   7.262%   $93.2858   $93.29   $93.30   $93.30  
  Purchase #5 $239.47   12.448%   $269.2792   $269.28   $269.30   $269.30  
  Purchase #6 $189.78   11.359%   $211.3371   $211.34   $211.35   $211.30  
  Purchase #7 $19.53   6.628%   $20.8244   $20.82   $20.80   $20.80  
  7 purchase totals = $1,053.15       $1,152.7048   $1,152.71   $1,152.70   $1,152.70