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 $83.65   3.578%   $86.643   $86.64   $86.65   $86.60  
  Purchase #2 $120.38   4.320%   $125.5804   $125.58   $125.60   $125.60  
  Purchase #3 $50.28   7.658%   $54.1304   $54.13   $54.15   $54.10  
  Purchase #4 $189.68   4.264%   $197.768   $197.77   $197.75   $197.80  
  Purchase #5 $126.50   8.653%   $137.446   $137.45   $137.45   $137.40  
  Purchase #6 $180.63   5.277%   $190.1618   $190.16   $190.15   $190.20  
  Purchase #7 $83.71   4.150%   $87.184   $87.18   $87.20   $87.20  
  7 purchase totals = $834.83       $878.9136   $878.91   $878.95   $878.90