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 $55.97   11.116%   $62.1916   $62.19   $62.20   $62.20  
  Purchase #2 $74.69   12.366%   $83.9262   $83.93   $83.95   $83.90  
  Purchase #3 $91.96   12.547%   $103.4982   $103.50   $103.50   $103.50  
  Purchase #4 $231.63   6.310%   $246.2459   $246.25   $246.25   $246.20  
  Purchase #5 $66.66   7.188%   $71.4515   $71.45   $71.45   $71.50  
  Purchase #6 $27.53   6.160%   $29.2258   $29.23   $29.25   $29.20  
  Purchase #7 $230.59   9.791%   $253.1671   $253.17   $253.15   $253.20  
  7 purchase totals = $779.03       $849.7063   $849.72   $849.75   $849.70