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 $157.70   11.240%   $175.4255   $175.43   $175.45   $175.40  
  Purchase #2 $167.36   12.290%   $187.9285   $187.93   $187.95   $187.90  
  Purchase #3 $158.90   9.461%   $173.9335   $173.93   $173.95   $173.90  
  Purchase #4 $43.36   9.109%   $47.3097   $47.31   $47.30   $47.30  
  Purchase #5 $124.71   6.756%   $133.1354   $133.14   $133.15   $133.10  
  Purchase #6 $88.52   6.211%   $94.018   $94.02   $94.00   $94.00  
  Purchase #7 $33.27   12.560%   $37.4487   $37.45   $37.45   $37.40  
  7 purchase totals = $773.82       $849.1993   $849.21   $849.25   $849.00