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 $184.69   10.443%   $203.9772   $203.98   $204.00   $204.00  
  Purchase #2 $245.78   8.219%   $265.9807   $265.98   $266.00   $266.00  
  Purchase #3 $76.95   10.431%   $84.9767   $84.98   $85.00   $85.00  
  Purchase #4 $89.42   11.364%   $99.5817   $99.58   $99.60   $99.60  
  Purchase #5 $146.27   11.346%   $162.8658   $162.87   $162.85   $162.90  
  Purchase #6 $129.50   3.376%   $133.8719   $133.87   $133.85   $133.90  
  Purchase #7 $92.56   9.121%   $101.0024   $101.00   $101.00   $101.00  
  7 purchase totals = $965.17       $1,052.2564   $1,052.26   $1,052.30   $1,052.40