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 $104.88   13.845%   $119.4006   $119.40   $119.40   $119.40  
  Purchase #2 $211.60   12.176%   $237.3644   $237.36   $237.35   $237.40  
  Purchase #3 $23.31   7.382%   $25.0307   $25.03   $25.05   $25.00  
  Purchase #4 $84.91   7.816%   $91.5466   $91.55   $91.55   $91.50  
  Purchase #5 $146.67   10.163%   $161.5761   $161.58   $161.60   $161.60  
  Purchase #6 $171.42   6.445%   $182.468   $182.47   $182.45   $182.50  
  Purchase #7 $200.56   9.361%   $219.3344   $219.33   $219.35   $219.30  
  7 purchase totals = $943.35       $1,036.7208   $1,036.72   $1,036.75   $1,036.70