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 $224.92   13.323%   $254.8861   $254.89   $254.90   $254.90  
  Purchase #2 $46.78   3.122%   $48.2405   $48.24   $48.25   $48.20  
  Purchase #3 $39.54   9.456%   $43.2789   $43.28   $43.30   $43.30  
  Purchase #4 $33.79   13.475%   $38.3432   $38.34   $38.35   $38.30  
  Purchase #5 $219.70   11.177%   $244.2559   $244.26   $244.25   $244.30  
  Purchase #6 $54.64   4.645%   $57.178   $57.18   $57.20   $57.20  
  Purchase #7 $250.26   12.283%   $280.9994   $281.00   $281.00   $281.00  
  7 purchase totals = $869.63       $967.1820   $967.19   $967.25   $967.20