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 $65.42   9.586%   $71.6912   $71.69   $71.70   $71.70  
  Purchase #2 $14.26   3.853%   $14.8094   $14.81   $14.80   $14.80  
  Purchase #3 $114.25   5.462%   $120.4903   $120.49   $120.50   $120.50  
  Purchase #4 $225.59   9.501%   $247.0233   $247.02   $247.00   $247.00  
  Purchase #5 $85.46   9.515%   $93.5915   $93.59   $93.60   $93.60  
  Purchase #6 $104.36   8.158%   $112.8737   $112.87   $112.85   $112.90  
  Purchase #7 $136.48   8.257%   $147.7492   $147.75   $147.75   $147.70  
  7 purchase totals = $745.82       $808.2286   $808.22   $808.20   $808.20