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 $175.57   12.544%   $197.5935   $197.59   $197.60   $197.60  
  Purchase #2 $190.75   4.624%   $199.5703   $199.57   $199.55   $199.60  
  Purchase #3 $87.60   12.646%   $98.6779   $98.68   $98.70   $98.70  
  Purchase #4 $48.31   3.323%   $49.9153   $49.92   $49.90   $49.90  
  Purchase #5 $5.74   6.526%   $6.1146   $6.11   $6.10   $6.10  
  Purchase #6 $47.82   4.645%   $50.0412   $50.04   $50.05   $50.00  
  Purchase #7 $200.91   7.690%   $216.36   $216.36   $216.35   $216.40  
  7 purchase totals = $756.70       $818.2728   $818.27   $818.25   $818.30