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 $75.74   8.284%   $82.0143   $82.01   $82.00   $82.00  
  Purchase #2 $245.71   9.384%   $268.7674   $268.77   $268.75   $268.80  
  Purchase #3 $239.81   13.679%   $272.6136   $272.61   $272.60   $272.60  
  Purchase #4 $59.79   10.682%   $66.1768   $66.18   $66.20   $66.20  
  Purchase #5 $43.26   10.803%   $47.9334   $47.93   $47.95   $47.90  
  Purchase #6 $45.67   6.359%   $48.5742   $48.57   $48.55   $48.60  
  Purchase #7 $38.25   4.857%   $40.1078   $40.11   $40.10   $40.10  
  7 purchase totals = $748.23       $826.1875   $826.18   $826.15   $826.20