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 $238.77   11.644%   $266.5724   $266.57   $266.55   $266.60  
  Purchase #2 $48.61   5.327%   $51.1995   $51.20   $51.20   $51.20  
  Purchase #3 $244.87   13.245%   $277.303   $277.30   $277.30   $277.30  
  Purchase #4 $32.82   8.187%   $35.507   $35.51   $35.50   $35.50  
  Purchase #5 $56.56   11.444%   $63.0327   $63.03   $63.05   $63.00  
  Purchase #6 $97.98   12.472%   $110.2001   $110.20   $110.20   $110.20  
  Purchase #7 $90.85   3.418%   $93.9553   $93.96   $93.95   $94.00  
  7 purchase totals = $810.46       $897.7700   $897.77   $897.75   $897.80