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 $61.44   13.183%   $69.5396   $69.54   $69.55   $69.50  
  Purchase #2 $26.84   5.529%   $28.324   $28.32   $28.30   $28.30  
  Purchase #3 $11.55   3.290%   $11.93   $11.93   $11.95   $11.90  
  Purchase #4 $244.47   8.539%   $265.3453   $265.35   $265.35   $265.30  
  Purchase #5 $138.98   7.622%   $149.5731   $149.57   $149.55   $149.60  
  Purchase #6 $154.57   11.669%   $172.6068   $172.61   $172.60   $172.60  
  Purchase #7 $151.72   7.571%   $163.2067   $163.21   $163.20   $163.20  
  7 purchase totals = $789.57       $860.5255   $860.53   $860.50   $860.40