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 $69.55   9.108%   $75.8846   $75.88   $75.90   $75.90  
  Purchase #2 $16.67   5.177%   $17.533   $17.53   $17.55   $17.50  
  Purchase #3 $47.95   11.790%   $53.6033   $53.60   $53.60   $53.60  
  Purchase #4 $103.88   7.714%   $111.8933   $111.89   $111.90   $111.90  
  Purchase #5 $72.60   6.288%   $77.1651   $77.17   $77.15   $77.20  
  Purchase #6 $249.26   9.324%   $272.501   $272.50   $272.50   $272.50  
  Purchase #7 $136.27   4.164%   $141.9443   $141.94   $141.95   $141.90  
  7 purchase totals = $696.18       $750.5246   $750.51   $750.55   $750.50