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 $71.96   6.594%   $76.705   $76.71   $76.70   $76.70  
  Purchase #2 $49.42   11.537%   $55.1216   $55.12   $55.10   $55.10  
  Purchase #3 $86.27   13.374%   $97.8077   $97.81   $97.80   $97.80  
  Purchase #4 $219.95   8.510%   $238.6677   $238.67   $238.65   $238.70  
  Purchase #5 $245.63   5.564%   $259.2969   $259.30   $259.30   $259.30  
  Purchase #6 $110.34   9.352%   $120.659   $120.66   $120.65   $120.70  
  Purchase #7 $152.39   13.700%   $173.2674   $173.27   $173.25   $173.30  
  7 purchase totals = $935.96       $1,021.5253   $1,021.54   $1,021.45   $1,021.60