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 $44.98   12.545%   $50.6227   $50.62   $50.60   $50.60  
  Purchase #2 $138.68   3.351%   $143.3272   $143.33   $143.35   $143.30  
  Purchase #3 $126.95   13.399%   $143.96   $143.96   $143.95   $144.00  
  Purchase #4 $115.31   9.774%   $126.5804   $126.58   $126.60   $126.60  
  Purchase #5 $190.78   3.310%   $197.0948   $197.09   $197.10   $197.10  
  Purchase #6 $130.72   12.120%   $146.5633   $146.56   $146.55   $146.60  
  Purchase #7 $208.59   9.140%   $227.6551   $227.66   $227.65   $227.70  
  7 purchase totals = $956.01       $1,035.8035   $1,035.80   $1,035.80   $1,035.90