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 $180.53   6.459%   $192.1904   $192.19   $192.20   $192.20  
  Purchase #2 $225.78   13.365%   $255.9555   $255.96   $255.95   $256.00  
  Purchase #3 $137.48   13.514%   $156.059   $156.06   $156.05   $156.10  
  Purchase #4 $244.80   9.765%   $268.7047   $268.70   $268.70   $268.70  
  Purchase #5 $68.77   6.555%   $73.2779   $73.28   $73.30   $73.30  
  Purchase #6 $59.99   12.369%   $67.4102   $67.41   $67.40   $67.40  
  Purchase #7 $18.41   7.849%   $19.855   $19.86   $19.85   $19.90  
  7 purchase totals = $935.76       $1,033.4527   $1,033.46   $1,033.45   $1,033.60