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 $146.99   4.322%   $153.3429   $153.34   $153.35   $153.30  
  Purchase #2 $201.26   4.813%   $210.9466   $210.95   $210.95   $210.90  
  Purchase #3 $43.36   12.430%   $48.7496   $48.75   $48.75   $48.70  
  Purchase #4 $224.48   3.169%   $231.5938   $231.59   $231.60   $231.60  
  Purchase #5 $79.28   7.572%   $85.2831   $85.28   $85.30   $85.30  
  Purchase #6 $239.63   11.847%   $268.019   $268.02   $268.00   $268.00  
  Purchase #7 $45.81   11.874%   $51.2495   $51.25   $51.25   $51.20  
  7 purchase totals = $980.81       $1,049.1845   $1,049.18   $1,049.20   $1,049.00