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 $176.98   12.766%   $199.5733   $199.57   $199.55   $199.60  
  Purchase #2 $154.76   8.864%   $168.4779   $168.48   $168.50   $168.50  
  Purchase #3 $87.65   10.155%   $96.5509   $96.55   $96.55   $96.60  
  Purchase #4 $46.33   5.611%   $48.9296   $48.93   $48.95   $48.90  
  Purchase #5 $246.95   8.507%   $267.958   $267.96   $267.95   $268.00  
  Purchase #6 $233.92   4.755%   $245.0429   $245.04   $245.05   $245.00  
  Purchase #7 $44.96   7.141%   $48.1706   $48.17   $48.15   $48.20  
  7 purchase totals = $991.55       $1,074.7032   $1,074.70   $1,074.70   $1,074.80