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 $86.51   6.227%   $91.897   $91.90   $91.90   $91.90  
  Purchase #2 $180.57   11.340%   $201.0466   $201.05   $201.05   $201.00  
  Purchase #3 $43.64   6.702%   $46.5648   $46.56   $46.55   $46.60  
  Purchase #4 $169.82   12.210%   $190.555   $190.56   $190.55   $190.60  
  Purchase #5 $221.50   9.629%   $242.8282   $242.83   $242.85   $242.80  
  Purchase #6 $84.82   9.450%   $92.8355   $92.84   $92.85   $92.80  
  Purchase #7 $97.53   3.232%   $100.6822   $100.68   $100.70   $100.70  
  7 purchase totals = $884.39       $966.4093   $966.42   $966.45   $966.40