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 $198.62   13.154%   $224.7465   $224.75   $224.75   $224.70  
  Purchase #2 $165.25   10.358%   $182.3666   $182.37   $182.35   $182.40  
  Purchase #3 $141.50   5.320%   $149.0278   $149.03   $149.05   $149.00  
  Purchase #4 $239.67   3.308%   $247.5983   $247.60   $247.60   $247.60  
  Purchase #5 $196.28   3.680%   $203.5031   $203.50   $203.50   $203.50  
  Purchase #6 $106.29   3.696%   $110.2185   $110.22   $110.20   $110.20  
  Purchase #7 $117.96   12.747%   $132.9964   $133.00   $133.00   $133.00  
  7 purchase totals = $1,165.57       $1,250.4572   $1,250.47   $1,250.45   $1,250.40