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 $215.26   6.558%   $229.3768   $229.38   $229.40   $229.40  
  Purchase #2 $231.55   6.368%   $246.2951   $246.30   $246.30   $246.30  
  Purchase #3 $56.76   3.865%   $58.9538   $58.95   $58.95   $59.00  
  Purchase #4 $125.55   4.486%   $131.1822   $131.18   $131.20   $131.20  
  Purchase #5 $24.97   5.858%   $26.4327   $26.43   $26.45   $26.40  
  Purchase #6 $161.43   7.534%   $173.5921   $173.59   $173.60   $173.60  
  Purchase #7 $6.67   4.285%   $6.9558   $6.96   $6.95   $7.00  
  7 purchase totals = $822.19       $872.7885   $872.79   $872.85   $872.90