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 $67.28   12.453%   $75.6584   $75.66   $75.65   $75.70  
  Purchase #2 $88.53   8.172%   $95.7647   $95.76   $95.75   $95.80  
  Purchase #3 $174.74   8.164%   $189.0058   $189.01   $189.00   $189.00  
  Purchase #4 $88.98   13.224%   $100.7467   $100.75   $100.75   $100.70  
  Purchase #5 $130.43   9.563%   $142.903   $142.90   $142.90   $142.90  
  Purchase #6 $223.80   10.253%   $246.7462   $246.75   $246.75   $246.70  
  Purchase #7 $118.69   5.401%   $125.1004   $125.10   $125.10   $125.10  
  7 purchase totals = $892.45       $975.9252   $975.93   $975.90   $975.90