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 $61.93   9.393%   $67.7471   $67.75   $67.75   $67.70  
  Purchase #2 $72.28   9.278%   $78.9861   $78.99   $79.00   $79.00  
  Purchase #3 $187.76   9.772%   $206.1079   $206.11   $206.10   $206.10  
  Purchase #4 $180.50   7.394%   $193.8462   $193.85   $193.85   $193.80  
  Purchase #5 $45.63   6.765%   $48.7169   $48.72   $48.70   $48.70  
  Purchase #6 $185.45   3.166%   $191.3213   $191.32   $191.30   $191.30  
  Purchase #7 $145.70   5.628%   $153.9   $153.90   $153.90   $153.90  
  7 purchase totals = $879.25       $940.6255   $940.64   $940.60   $940.50