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 $222.69   4.471%   $232.6465   $232.65   $232.65   $232.60  
  Purchase #2 $228.58   12.591%   $257.3605   $257.36   $257.35   $257.40  
  Purchase #3 $52.53   7.594%   $56.5191   $56.52   $56.50   $56.50  
  Purchase #4 $14.96   11.754%   $16.7184   $16.72   $16.70   $16.70  
  Purchase #5 $161.86   10.763%   $179.281   $179.28   $179.30   $179.30  
  Purchase #6 $224.49   6.832%   $239.8272   $239.83   $239.85   $239.80  
  Purchase #7 $25.89   13.526%   $29.3919   $29.39   $29.40   $29.40  
  7 purchase totals = $931.00       $1,011.7446   $1,011.75   $1,011.75   $1,011.70