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 $93.95   10.203%   $103.5357   $103.54   $103.55   $103.50  
  Purchase #2 $68.66   10.208%   $75.6688   $75.67   $75.65   $75.70  
  Purchase #3 $55.85   7.372%   $59.9673   $59.97   $59.95   $60.00  
  Purchase #4 $134.46   6.441%   $143.1206   $143.12   $143.10   $143.10  
  Purchase #5 $192.58   5.768%   $203.688   $203.69   $203.70   $203.70  
  Purchase #6 $146.63   9.199%   $160.1185   $160.12   $160.10   $160.10  
  Purchase #7 $97.59   5.814%   $103.2639   $103.26   $103.25   $103.30  
  7 purchase totals = $789.72       $849.3628   $849.37   $849.30   $849.40