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 $218.87   6.802%   $233.7575   $233.76   $233.75   $233.80  
  Purchase #2 $111.48   4.362%   $116.3428   $116.34   $116.35   $116.30  
  Purchase #3 $237.71   6.449%   $253.0399   $253.04   $253.05   $253.00  
  Purchase #4 $144.96   4.352%   $151.2687   $151.27   $151.25   $151.30  
  Purchase #5 $60.69   12.755%   $68.431   $68.43   $68.45   $68.40  
  Purchase #6 $106.93   10.132%   $117.7641   $117.76   $117.75   $117.80  
  Purchase #7 $96.73   7.119%   $103.6162   $103.62   $103.60   $103.60  
  7 purchase totals = $977.37       $1,044.2202   $1,044.22   $1,044.20   $1,044.20