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 $22.53   13.683%   $25.6128   $25.61   $25.60   $25.60  
  Purchase #2 $196.55   3.551%   $203.5295   $203.53   $203.55   $203.50  
  Purchase #3 $7.93   13.599%   $9.0084   $9.01   $9.00   $9.00  
  Purchase #4 $82.64   13.416%   $93.727   $93.73   $93.75   $93.70  
  Purchase #5 $208.66   8.296%   $225.9704   $225.97   $225.95   $226.00  
  Purchase #6 $205.30   3.174%   $211.8162   $211.82   $211.80   $211.80  
  Purchase #7 $215.41   13.194%   $243.8312   $243.83   $243.85   $243.80  
  7 purchase totals = $939.02       $1,013.4955   $1,013.50   $1,013.50   $1,013.40