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 $189.77   11.207%   $211.0375   $211.04   $211.05   $211.00  
  Purchase #2 $90.27   9.333%   $98.6949   $98.69   $98.70   $98.70  
  Purchase #3 $173.58   4.766%   $181.8528   $181.85   $181.85   $181.90  
  Purchase #4 $94.26   3.549%   $97.6053   $97.61   $97.60   $97.60  
  Purchase #5 $243.91   5.867%   $258.2202   $258.22   $258.20   $258.20  
  Purchase #6 $32.70   5.863%   $34.6172   $34.62   $34.60   $34.60  
  Purchase #7 $120.65   11.824%   $134.9157   $134.92   $134.90   $134.90  
  7 purchase totals = $945.14       $1,016.9436   $1,016.95   $1,016.90   $1,016.90