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 $59.30   8.530%   $64.3583   $64.36   $64.35   $64.40  
  Purchase #2 $233.39   4.580%   $244.0793   $244.08   $244.10   $244.10  
  Purchase #3 $235.70   4.426%   $246.1321   $246.13   $246.15   $246.10  
  Purchase #4 $46.69   8.461%   $50.6404   $50.64   $50.65   $50.60  
  Purchase #5 $136.47   3.228%   $140.8753   $140.88   $140.90   $140.90  
  Purchase #6 $207.84   3.557%   $215.2329   $215.23   $215.25   $215.20  
  Purchase #7 $59.77   4.263%   $62.318   $62.32   $62.30   $62.30  
  7 purchase totals = $979.16       $1,023.6363   $1,023.64   $1,023.70   $1,023.60