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 $206.90   8.477%   $224.4389   $224.44   $224.45   $224.40  
  Purchase #2 $217.60   6.554%   $231.8615   $231.86   $231.85   $231.90  
  Purchase #3 $168.34   12.242%   $188.9482   $188.95   $188.95   $188.90  
  Purchase #4 $237.67   9.833%   $261.0401   $261.04   $261.05   $261.00  
  Purchase #5 $201.65   5.415%   $212.5693   $212.57   $212.55   $212.60  
  Purchase #6 $207.42   8.622%   $225.3038   $225.30   $225.30   $225.30  
  Purchase #7 $21.89   13.365%   $24.8156   $24.82   $24.80   $24.80  
  7 purchase totals = $1,261.47       $1,368.9774   $1,368.98   $1,368.95   $1,368.90