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 $249.78   9.657%   $273.9013   $273.90   $273.90   $273.90  
  Purchase #2 $97.93   3.355%   $101.2156   $101.22   $101.20   $101.20  
  Purchase #3 $198.85   3.674%   $206.1557   $206.16   $206.15   $206.20  
  Purchase #4 $76.59   11.700%   $85.551   $85.55   $85.55   $85.60  
  Purchase #5 $196.33   4.381%   $204.9312   $204.93   $204.95   $204.90  
  Purchase #6 $215.68   6.144%   $228.9314   $228.93   $228.95   $228.90  
  Purchase #7 $63.29   5.154%   $66.552   $66.55   $66.55   $66.60  
  7 purchase totals = $1,098.45       $1,167.2382   $1,167.24   $1,167.25   $1,167.30