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 $104.69   10.687%   $115.8782   $115.88   $115.90   $115.90  
  Purchase #2 $201.42   11.237%   $224.0536   $224.05   $224.05   $224.10  
  Purchase #3 $123.53   7.259%   $132.497   $132.50   $132.50   $132.50  
  Purchase #4 $174.85   6.334%   $185.925   $185.93   $185.95   $185.90  
  Purchase #5 $18.58   5.723%   $19.6433   $19.64   $19.65   $19.60  
  Purchase #6 $134.45   11.290%   $149.6294   $149.63   $149.65   $149.60  
  Purchase #7 $210.51   10.676%   $232.984   $232.98   $233.00   $233.00  
  7 purchase totals = $968.03       $1,060.6105   $1,060.61   $1,060.70   $1,060.60