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 $139.69   10.205%   $153.9454   $153.95   $153.95   $153.90  
  Purchase #2 $236.72   13.365%   $268.3576   $268.36   $268.35   $268.40  
  Purchase #3 $190.65   6.853%   $203.7152   $203.72   $203.70   $203.70  
  Purchase #4 $214.87   10.864%   $238.2135   $238.21   $238.20   $238.20  
  Purchase #5 $59.46   4.389%   $62.0697   $62.07   $62.05   $62.10  
  Purchase #6 $201.68   7.258%   $216.3179   $216.32   $216.30   $216.30  
  Purchase #7 $181.75   5.619%   $191.9625   $191.96   $191.95   $192.00  
  7 purchase totals = $1,224.82       $1,334.5818   $1,334.59   $1,334.50   $1,334.60