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 $211.53   12.322%   $237.5947   $237.59   $237.60   $237.60  
  Purchase #2 $22.93   11.771%   $25.6291   $25.63   $25.65   $25.60  
  Purchase #3 $64.74   11.644%   $72.2783   $72.28   $72.30   $72.30  
  Purchase #4 $85.97   10.154%   $94.6994   $94.70   $94.70   $94.70  
  Purchase #5 $81.40   5.535%   $85.9055   $85.91   $85.90   $85.90  
  Purchase #6 $219.29   7.387%   $235.489   $235.49   $235.50   $235.50  
  Purchase #7 $197.46   5.681%   $208.6777   $208.68   $208.70   $208.70  
  7 purchase totals = $883.32       $960.2737   $960.28   $960.35   $960.30