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 $18.82   3.402%   $19.4603   $19.46   $19.45   $19.50  
  Purchase #2 $219.94   13.287%   $249.1634   $249.16   $249.15   $249.20  
  Purchase #3 $167.89   5.103%   $176.4574   $176.46   $176.45   $176.50  
  Purchase #4 $67.98   4.407%   $70.9759   $70.98   $71.00   $71.00  
  Purchase #5 $243.76   6.530%   $259.6775   $259.68   $259.70   $259.70  
  Purchase #6 $250.96   6.645%   $267.6363   $267.64   $267.65   $267.60  
  Purchase #7 $16.36   13.840%   $18.6242   $18.62   $18.60   $18.60  
  7 purchase totals = $985.71       $1,061.9950   $1,062.00   $1,062.00   $1,062.10