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 $65.26   4.804%   $68.3951   $68.40   $68.40   $68.40  
  Purchase #2 $121.36   4.561%   $126.8952   $126.90   $126.90   $126.90  
  Purchase #3 $208.56   7.820%   $224.8694   $224.87   $224.85   $224.90  
  Purchase #4 $114.98   3.851%   $119.4079   $119.41   $119.40   $119.40  
  Purchase #5 $124.65   8.632%   $135.4098   $135.41   $135.40   $135.40  
  Purchase #6 $123.57   5.521%   $130.3923   $130.39   $130.40   $130.40  
  Purchase #7 $187.78   4.202%   $195.6705   $195.67   $195.65   $195.70  
  7 purchase totals = $946.16       $1,001.0402   $1,001.05   $1,001.00   $1,001.10