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 $29.56   8.402%   $32.0436   $32.04   $32.05   $32.00  
  Purchase #2 $197.75   8.503%   $214.5647   $214.56   $214.55   $214.60  
  Purchase #3 $157.67   7.336%   $169.2367   $169.24   $169.25   $169.20  
  Purchase #4 $32.83   6.602%   $34.9974   $35.00   $35.00   $35.00  
  Purchase #5 $225.39   11.590%   $251.5127   $251.51   $251.50   $251.50  
  Purchase #6 $61.90   7.286%   $66.41   $66.41   $66.40   $66.40  
  Purchase #7 $209.97   7.456%   $225.6254   $225.63   $225.65   $225.60  
  7 purchase totals = $915.07       $994.3905   $994.39   $994.40   $994.30