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 $88.81   8.674%   $96.5134   $96.51   $96.50   $96.50  
  Purchase #2 $67.77   11.352%   $75.4633   $75.46   $75.45   $75.50  
  Purchase #3 $54.99   6.659%   $58.6518   $58.65   $58.65   $58.70  
  Purchase #4 $204.46   6.325%   $217.3921   $217.39   $217.40   $217.40  
  Purchase #5 $200.50   13.375%   $227.3169   $227.32   $227.30   $227.30  
  Purchase #6 $231.95   7.779%   $249.9934   $249.99   $250.00   $250.00  
  Purchase #7 $13.28   10.780%   $14.7116   $14.71   $14.70   $14.70  
  7 purchase totals = $861.76       $940.0425   $940.03   $940.00   $940.10