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 $23.62   10.442%   $26.0864   $26.09   $26.10   $26.10  
  Purchase #2 $215.76   13.685%   $245.2868   $245.29   $245.30   $245.30  
  Purchase #3 $59.73   7.798%   $64.3877   $64.39   $64.40   $64.40  
  Purchase #4 $187.50   13.817%   $213.4069   $213.41   $213.40   $213.40  
  Purchase #5 $167.76   4.778%   $175.7756   $175.78   $175.80   $175.80  
  Purchase #6 $169.68   8.121%   $183.4597   $183.46   $183.45   $183.50  
  Purchase #7 $86.82   9.270%   $94.8682   $94.87   $94.85   $94.90  
  7 purchase totals = $910.87       $1,003.2713   $1,003.29   $1,003.30   $1,003.40