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 $61.82   7.317%   $66.3434   $66.34   $66.35   $66.30  
  Purchase #2 $217.99   3.424%   $225.454   $225.45   $225.45   $225.50  
  Purchase #3 $12.32   4.751%   $12.9053   $12.91   $12.90   $12.90  
  Purchase #4 $44.42   13.531%   $50.4305   $50.43   $50.45   $50.40  
  Purchase #5 $120.43   10.118%   $132.6151   $132.62   $132.60   $132.60  
  Purchase #6 $226.62   8.245%   $245.3048   $245.30   $245.30   $245.30  
  Purchase #7 $101.94   13.187%   $115.3828   $115.38   $115.40   $115.40  
  7 purchase totals = $785.54       $848.4359   $848.43   $848.45   $848.40