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 $66.93   11.614%   $74.7033   $74.70   $74.70   $74.70  
  Purchase #2 $180.38   7.479%   $193.8706   $193.87   $193.85   $193.90  
  Purchase #3 $84.95   9.667%   $93.1621   $93.16   $93.15   $93.20  
  Purchase #4 $93.58   5.407%   $98.6399   $98.64   $98.65   $98.60  
  Purchase #5 $250.43   7.208%   $268.481   $268.48   $268.50   $268.50  
  Purchase #6 $159.88   3.202%   $164.9994   $165.00   $165.00   $165.00  
  Purchase #7 $35.53   6.223%   $37.741   $37.74   $37.75   $37.70  
  7 purchase totals = $871.68       $931.5973   $931.59   $931.60   $931.60