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 $197.80   5.152%   $207.9907   $207.99   $208.00   $208.00  
  Purchase #2 $51.50   4.791%   $53.9674   $53.97   $53.95   $54.00  
  Purchase #3 $200.38   4.694%   $209.7858   $209.79   $209.80   $209.80  
  Purchase #4 $114.38   11.667%   $127.7247   $127.72   $127.70   $127.70  
  Purchase #5 $70.65   3.350%   $73.0168   $73.02   $73.00   $73.00  
  Purchase #6 $235.29   11.239%   $261.7342   $261.73   $261.75   $261.70  
  Purchase #7 $37.43   5.128%   $39.3494   $39.35   $39.35   $39.30  
  7 purchase totals = $907.43       $973.5690   $973.57   $973.55   $973.50