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 $73.46   3.279%   $75.8688   $75.87   $75.85   $75.90  
  Purchase #2 $54.72   3.313%   $56.5329   $56.53   $56.55   $56.50  
  Purchase #3 $66.99   11.290%   $74.5532   $74.55   $74.55   $74.60  
  Purchase #4 $143.97   8.689%   $156.4796   $156.48   $156.50   $156.50  
  Purchase #5 $6.72   3.342%   $6.9446   $6.94   $6.95   $6.90  
  Purchase #6 $208.60   10.527%   $230.5593   $230.56   $230.55   $230.60  
  Purchase #7 $216.85   11.140%   $241.0071   $241.01   $241.00   $241.00  
  7 purchase totals = $771.31       $841.9455   $841.94   $841.95   $842.00