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 $234.32   8.727%   $254.7691   $254.77   $254.75   $254.80  
  Purchase #2 $38.35   12.646%   $43.1997   $43.20   $43.20   $43.20  
  Purchase #3 $91.82   7.476%   $98.6845   $98.68   $98.70   $98.70  
  Purchase #4 $61.26   8.685%   $66.5804   $66.58   $66.60   $66.60  
  Purchase #5 $111.82   12.394%   $125.679   $125.68   $125.70   $125.70  
  Purchase #6 $56.59   11.644%   $63.1793   $63.18   $63.20   $63.20  
  Purchase #7 $105.36   5.663%   $111.3265   $111.33   $111.35   $111.30  
  7 purchase totals = $699.52       $763.4185   $763.42   $763.50   $763.50