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 $24.67   6.701%   $26.3231   $26.32   $26.30   $26.30  
  Purchase #2 $224.51   3.861%   $233.1783   $233.18   $233.20   $233.20  
  Purchase #3 $28.41   8.257%   $30.7558   $30.76   $30.75   $30.80  
  Purchase #4 $96.37   12.206%   $108.1329   $108.13   $108.15   $108.10  
  Purchase #5 $106.70   11.789%   $119.2789   $119.28   $119.30   $119.30  
  Purchase #6 $164.75   5.806%   $174.3154   $174.32   $174.30   $174.30  
  Purchase #7 $114.55   5.241%   $120.5536   $120.55   $120.55   $120.60  
  7 purchase totals = $759.96       $812.5380   $812.54   $812.55   $812.60