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 $207.59   11.417%   $231.2906   $231.29   $231.30   $231.30  
  Purchase #2 $117.63   11.837%   $131.5539   $131.55   $131.55   $131.60  
  Purchase #3 $199.43   10.703%   $220.775   $220.78   $220.80   $220.80  
  Purchase #4 $182.72   5.313%   $192.4279   $192.43   $192.45   $192.40  
  Purchase #5 $148.28   7.207%   $158.9665   $158.97   $158.95   $159.00  
  Purchase #6 $61.55   7.725%   $66.3047   $66.30   $66.30   $66.30  
  Purchase #7 $71.80   6.769%   $76.6601   $76.66   $76.65   $76.70  
  7 purchase totals = $989.00       $1,077.9787   $1,077.98   $1,078.00   $1,078.10