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 $24.57   6.518%   $26.1715   $26.17   $26.15   $26.20  
  Purchase #2 $62.27   3.254%   $64.2963   $64.30   $64.30   $64.30  
  Purchase #3 $9.27   7.648%   $9.979   $9.98   $10.00   $10.00  
  Purchase #4 $59.95   4.419%   $62.5992   $62.60   $62.60   $62.60  
  Purchase #5 $103.40   9.783%   $113.5156   $113.52   $113.50   $113.50  
  Purchase #6 $203.67   12.275%   $228.6705   $228.67   $228.65   $228.70  
  Purchase #7 $94.66   11.438%   $105.4872   $105.49   $105.50   $105.50  
  7 purchase totals = $557.79       $610.7193   $610.73   $610.70   $610.80