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 $163.64   11.436%   $182.3539   $182.35   $182.35   $182.40  
  Purchase #2 $228.99   3.712%   $237.4901   $237.49   $237.50   $237.50  
  Purchase #3 $94.66   7.608%   $101.8617   $101.86   $101.85   $101.90  
  Purchase #4 $179.67   9.780%   $197.2417   $197.24   $197.25   $197.20  
  Purchase #5 $85.68   7.254%   $91.8952   $91.90   $91.90   $91.90  
  Purchase #6 $101.25   11.389%   $112.7814   $112.78   $112.80   $112.80  
  Purchase #7 $127.40   4.489%   $133.119   $133.12   $133.10   $133.10  
  7 purchase totals = $981.29       $1,056.7430   $1,056.74   $1,056.75   $1,056.80