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 $116.37   8.529%   $126.2952   $126.30   $126.30   $126.30  
  Purchase #2 $113.98   7.423%   $122.4407   $122.44   $122.45   $122.40  
  Purchase #3 $147.46   13.171%   $166.882   $166.88   $166.90   $166.90  
  Purchase #4 $176.34   12.414%   $198.2308   $198.23   $198.25   $198.20  
  Purchase #5 $44.33   6.170%   $47.0652   $47.07   $47.05   $47.10  
  Purchase #6 $131.44   3.275%   $135.7447   $135.74   $135.75   $135.70  
  Purchase #7 $114.53   9.235%   $125.1068   $125.11   $125.10   $125.10  
  7 purchase totals = $844.45       $921.7654   $921.77   $921.80   $921.70