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 $23.79   6.266%   $25.2807   $25.28   $25.30   $25.30  
  Purchase #2 $108.74   10.208%   $119.8402   $119.84   $119.85   $119.80  
  Purchase #3 $94.47   8.168%   $102.1863   $102.19   $102.20   $102.20  
  Purchase #4 $204.59   10.466%   $226.0024   $226.00   $226.00   $226.00  
  Purchase #5 $64.28   4.701%   $67.3018   $67.30   $67.30   $67.30  
  Purchase #6 $159.45   5.295%   $167.8929   $167.89   $167.90   $167.90  
  Purchase #7 $52.95   4.820%   $55.5022   $55.50   $55.50   $55.50  
  7 purchase totals = $708.27       $764.0065   $764.00   $764.05   $764.00