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 $164.84   11.842%   $184.3604   $184.36   $184.35   $184.40  
  Purchase #2 $124.74   8.766%   $135.6747   $135.67   $135.65   $135.70  
  Purchase #3 $146.55   7.507%   $157.5515   $157.55   $157.55   $157.60  
  Purchase #4 $166.44   4.502%   $173.9331   $173.93   $173.95   $173.90  
  Purchase #5 $98.25   7.198%   $105.322   $105.32   $105.30   $105.30  
  Purchase #6 $159.75   11.388%   $177.9423   $177.94   $177.95   $177.90  
  Purchase #7 $60.73   11.371%   $67.6356   $67.64   $67.65   $67.60  
  7 purchase totals = $921.30       $1,002.4196   $1,002.41   $1,002.40   $1,002.40