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 $47.87   8.180%   $51.7858   $51.79   $51.80   $51.80  
  Purchase #2 $209.98   12.479%   $236.1834   $236.18   $236.20   $236.20  
  Purchase #3 $127.89   7.229%   $137.1352   $137.14   $137.15   $137.10  
  Purchase #4 $204.31   6.217%   $217.012   $217.01   $217.00   $217.00  
  Purchase #5 $102.67   13.688%   $116.7235   $116.72   $116.70   $116.70  
  Purchase #6 $32.71   11.804%   $36.5711   $36.57   $36.55   $36.60  
  Purchase #7 $219.86   7.611%   $236.5935   $236.59   $236.60   $236.60  
  7 purchase totals = $945.29       $1,032.0045   $1,032.00   $1,032.00   $1,032.00