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 $63.54   4.854%   $66.6242   $66.62   $66.60   $66.60  
  Purchase #2 $55.94   3.126%   $57.6887   $57.69   $57.70   $57.70  
  Purchase #3 $227.96   13.351%   $258.3949   $258.39   $258.40   $258.40  
  Purchase #4 $75.35   7.499%   $81.0005   $81.00   $81.00   $81.00  
  Purchase #5 $120.94   9.335%   $132.2297   $132.23   $132.25   $132.20  
  Purchase #6 $57.26   8.243%   $61.9799   $61.98   $62.00   $62.00  
  Purchase #7 $86.78   8.332%   $94.0105   $94.01   $94.00   $94.00  
  7 purchase totals = $687.77       $751.9284   $751.92   $751.95   $751.90