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 $66.58   13.791%   $75.762   $75.76   $75.75   $75.80  
  Purchase #2 $52.79   3.344%   $54.5553   $54.56   $54.55   $54.60  
  Purchase #3 $76.75   6.335%   $81.6121   $81.61   $81.60   $81.60  
  Purchase #4 $180.91   10.187%   $199.3393   $199.34   $199.35   $199.30  
  Purchase #5 $7.44   9.407%   $8.1399   $8.14   $8.15   $8.10  
  Purchase #6 $184.41   4.873%   $193.3963   $193.40   $193.40   $193.40  
  Purchase #7 $37.98   12.253%   $42.6337   $42.63   $42.65   $42.60  
  7 purchase totals = $606.86       $655.4386   $655.44   $655.45   $655.40