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 $84.48   13.408%   $95.8071   $95.81   $95.80   $95.80  
  Purchase #2 $197.85   13.824%   $225.2008   $225.20   $225.20   $225.20  
  Purchase #3 $72.33   10.830%   $80.1633   $80.16   $80.15   $80.20  
  Purchase #4 $244.30   11.457%   $272.2895   $272.29   $272.30   $272.30  
  Purchase #5 $72.45   5.771%   $76.6311   $76.63   $76.65   $76.60  
  Purchase #6 $115.73   5.501%   $122.0963   $122.10   $122.10   $122.10  
  Purchase #7 $117.41   7.856%   $126.6337   $126.63   $126.65   $126.60  
  7 purchase totals = $904.55       $998.8218   $998.82   $998.85   $998.80