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 $92.67   3.709%   $96.1071   $96.11   $96.10   $96.10  
  Purchase #2 $60.56   4.708%   $63.4112   $63.41   $63.40   $63.40  
  Purchase #3 $25.56   4.649%   $26.7483   $26.75   $26.75   $26.70  
  Purchase #4 $169.84   7.666%   $182.8599   $182.86   $182.85   $182.90  
  Purchase #5 $182.75   9.607%   $200.3068   $200.31   $200.30   $200.30  
  Purchase #6 $144.83   3.753%   $150.2655   $150.27   $150.25   $150.30  
  Purchase #7 $5.43   11.371%   $6.0474   $6.05   $6.05   $6.00  
  7 purchase totals = $681.64       $725.7462   $725.76   $725.70   $725.70