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 $119.41   4.314%   $124.5613   $124.56   $124.55   $124.60  
  Purchase #2 $40.39   8.866%   $43.971   $43.97   $43.95   $44.00  
  Purchase #3 $67.81   4.668%   $70.9754   $70.98   $71.00   $71.00  
  Purchase #4 $169.65   13.686%   $192.8683   $192.87   $192.85   $192.90  
  Purchase #5 $157.30   10.534%   $173.87   $173.87   $173.85   $173.90  
  Purchase #6 $54.95   9.523%   $60.1829   $60.18   $60.20   $60.20  
  Purchase #7 $7.43   13.648%   $8.444   $8.44   $8.45   $8.40  
  7 purchase totals = $616.94       $674.8729   $674.87   $674.85   $675.00