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 $224.27   9.691%   $246.004   $246.00   $246.00   $246.00  
  Purchase #2 $182.49   5.682%   $192.8591   $192.86   $192.85   $192.90  
  Purchase #3 $15.61   9.245%   $17.0531   $17.05   $17.05   $17.10  
  Purchase #4 $199.52   7.432%   $214.3483   $214.35   $214.35   $214.30  
  Purchase #5 $226.62   7.511%   $243.6414   $243.64   $243.65   $243.60  
  Purchase #6 $246.46   12.281%   $276.7278   $276.73   $276.75   $276.70  
  Purchase #7 $17.54   12.338%   $19.7041   $19.70   $19.70   $19.70  
  7 purchase totals = $1,112.51       $1,210.3378   $1,210.33   $1,210.35   $1,210.30