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 $182.45   4.480%   $190.6238   $190.62   $190.60   $190.60  
  Purchase #2 $9.82   10.196%   $10.8212   $10.82   $10.80   $10.80  
  Purchase #3 $99.83   8.489%   $108.3046   $108.30   $108.30   $108.30  
  Purchase #4 $73.98   7.314%   $79.3909   $79.39   $79.40   $79.40  
  Purchase #5 $78.49   3.820%   $81.4883   $81.49   $81.50   $81.50  
  Purchase #6 $190.46   13.624%   $216.4083   $216.41   $216.40   $216.40  
  Purchase #7 $82.87   6.554%   $88.3013   $88.30   $88.30   $88.30  
  7 purchase totals = $717.90       $775.3384   $775.33   $775.30   $775.30