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 $56.72   12.194%   $63.6364   $63.64   $63.65   $63.60  
  Purchase #2 $57.92   7.746%   $62.4065   $62.41   $62.40   $62.40  
  Purchase #3 $157.81   10.142%   $173.8151   $173.82   $173.80   $173.80  
  Purchase #4 $240.33   12.211%   $269.6767   $269.68   $269.70   $269.70  
  Purchase #5 $142.42   10.529%   $157.4154   $157.42   $157.40   $157.40  
  Purchase #6 $132.53   6.817%   $141.5646   $141.56   $141.55   $141.60  
  Purchase #7 $25.92   3.204%   $26.7505   $26.75   $26.75   $26.80  
  7 purchase totals = $813.65       $895.2652   $895.28   $895.25   $895.30