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 $109.89   4.213%   $114.5197   $114.52   $114.50   $114.50  
  Purchase #2 $215.55   9.616%   $236.2773   $236.28   $236.30   $236.30  
  Purchase #3 $168.62   5.441%   $177.7946   $177.79   $177.80   $177.80  
  Purchase #4 $65.62   11.170%   $72.9498   $72.95   $72.95   $72.90  
  Purchase #5 $134.74   11.866%   $150.7282   $150.73   $150.75   $150.70  
  Purchase #6 $246.49   12.545%   $277.4122   $277.41   $277.40   $277.40  
  Purchase #7 $62.92   3.654%   $65.2191   $65.22   $65.20   $65.20  
  7 purchase totals = $1,003.83       $1,094.9009   $1,094.90   $1,094.90   $1,094.80