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 $179.26   13.606%   $203.6501   $203.65   $203.65   $203.70  
  Purchase #2 $219.74   11.814%   $245.7001   $245.70   $245.70   $245.70  
  Purchase #3 $194.26   6.808%   $207.4852   $207.49   $207.50   $207.50  
  Purchase #4 $76.93   9.813%   $84.4791   $84.48   $84.50   $84.50  
  Purchase #5 $83.50   13.648%   $94.8961   $94.90   $94.90   $94.90  
  Purchase #6 $217.38   8.764%   $236.4312   $236.43   $236.45   $236.40  
  Purchase #7 $168.68   10.642%   $186.6309   $186.63   $186.65   $186.60  
  7 purchase totals = $1,139.75       $1,259.2727   $1,259.28   $1,259.35   $1,259.30