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 $91.61   11.666%   $102.2972   $102.30   $102.30   $102.30  
  Purchase #2 $234.56   6.556%   $249.9378   $249.94   $249.95   $249.90  
  Purchase #3 $160.89   13.435%   $182.5056   $182.51   $182.50   $182.50  
  Purchase #4 $68.54   6.862%   $73.2432   $73.24   $73.25   $73.20  
  Purchase #5 $169.48   6.693%   $180.8233   $180.82   $180.80   $180.80  
  Purchase #6 $186.98   9.565%   $204.8646   $204.86   $204.85   $204.90  
  Purchase #7 $219.82   11.762%   $245.6752   $245.68   $245.70   $245.70  
  7 purchase totals = $1,131.88       $1,239.3469   $1,239.35   $1,239.35   $1,239.30