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 $35.26   6.463%   $37.5389   $37.54   $37.55   $37.50  
  Purchase #2 $108.68   12.286%   $122.0324   $122.03   $122.05   $122.00  
  Purchase #3 $119.51   8.508%   $129.6779   $129.68   $129.70   $129.70  
  Purchase #4 $68.89   3.328%   $71.1827   $71.18   $71.20   $71.20  
  Purchase #5 $250.58   4.575%   $262.044   $262.04   $262.05   $262.00  
  Purchase #6 $113.98   8.330%   $123.4745   $123.47   $123.45   $123.50  
  Purchase #7 $142.96   9.180%   $156.0837   $156.08   $156.10   $156.10  
  7 purchase totals = $839.86       $902.0341   $902.02   $902.10   $902.00