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 $81.71   11.501%   $91.1075   $91.11   $91.10   $91.10  
  Purchase #2 $240.54   4.187%   $250.6114   $250.61   $250.60   $250.60  
  Purchase #3 $78.62   12.617%   $88.5395   $88.54   $88.55   $88.50  
  Purchase #4 $125.61   7.809%   $135.4189   $135.42   $135.40   $135.40  
  Purchase #5 $22.75   9.257%   $24.856   $24.86   $24.85   $24.90  
  Purchase #6 $185.90   6.290%   $197.5931   $197.59   $197.60   $197.60  
  Purchase #7 $215.87   13.362%   $244.7145   $244.71   $244.70   $244.70  
  7 purchase totals = $951.00       $1,032.8409   $1,032.84   $1,032.80   $1,032.80