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 $41.97   12.439%   $47.1906   $47.19   $47.20   $47.20  
  Purchase #2 $154.35   9.207%   $168.561   $168.56   $168.55   $168.60  
  Purchase #3 $69.75   13.251%   $78.9926   $78.99   $79.00   $79.00  
  Purchase #4 $152.84   4.651%   $159.9486   $159.95   $159.95   $159.90  
  Purchase #5 $244.53   8.188%   $264.5521   $264.55   $264.55   $264.60  
  Purchase #6 $176.36   12.197%   $197.8706   $197.87   $197.85   $197.90  
  Purchase #7 $41.83   6.293%   $44.4624   $44.46   $44.45   $44.50  
  7 purchase totals = $881.63       $961.5779   $961.57   $961.55   $961.70