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 $230.39   6.802%   $246.0611   $246.06   $246.05   $246.10  
  Purchase #2 $24.89   5.661%   $26.299   $26.30   $26.30   $26.30  
  Purchase #3 $51.47   5.297%   $54.1964   $54.20   $54.20   $54.20  
  Purchase #4 $45.49   9.348%   $49.7424   $49.74   $49.75   $49.70  
  Purchase #5 $51.65   10.810%   $57.2334   $57.23   $57.25   $57.20  
  Purchase #6 $117.64   12.208%   $132.0015   $132.00   $132.00   $132.00  
  Purchase #7 $80.93   9.791%   $88.8539   $88.85   $88.85   $88.90  
  7 purchase totals = $602.46       $654.3877   $654.38   $654.40   $654.40