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 $246.92   6.399%   $262.7204   $262.72   $262.70   $262.70  
  Purchase #2 $216.44   11.166%   $240.6077   $240.61   $240.60   $240.60  
  Purchase #3 $6.81   10.605%   $7.5322   $7.53   $7.55   $7.50  
  Purchase #4 $205.96   9.195%   $224.898   $224.90   $224.90   $224.90  
  Purchase #5 $99.41   8.668%   $108.0269   $108.03   $108.05   $108.00  
  Purchase #6 $146.52   9.326%   $160.1845   $160.18   $160.20   $160.20  
  Purchase #7 $71.96   6.535%   $76.6626   $76.66   $76.65   $76.70  
  7 purchase totals = $994.02       $1,080.6323   $1,080.63   $1,080.65   $1,080.60