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 $42.95   8.277%   $46.505   $46.51   $46.50   $46.50  
  Purchase #2 $134.31   3.197%   $138.6039   $138.60   $138.60   $138.60  
  Purchase #3 $195.42   10.676%   $216.283   $216.28   $216.30   $216.30  
  Purchase #4 $59.86   11.582%   $66.793   $66.79   $66.80   $66.80  
  Purchase #5 $193.59   6.191%   $205.5752   $205.58   $205.60   $205.60  
  Purchase #6 $217.57   6.575%   $231.8752   $231.88   $231.90   $231.90  
  Purchase #7 $68.80   6.488%   $73.2637   $73.26   $73.25   $73.30  
  7 purchase totals = $912.50       $978.8990   $978.90   $978.95   $979.00