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 $62.47   11.195%   $69.4635   $69.46   $69.45   $69.50  
  Purchase #2 $159.99   6.202%   $169.9126   $169.91   $169.90   $169.90  
  Purchase #3 $139.86   3.757%   $145.1145   $145.11   $145.10   $145.10  
  Purchase #4 $141.87   7.833%   $152.9827   $152.98   $153.00   $153.00  
  Purchase #5 $42.48   10.208%   $46.8164   $46.82   $46.80   $46.80  
  Purchase #6 $228.36   5.698%   $241.372   $241.37   $241.35   $241.40  
  Purchase #7 $163.87   4.463%   $171.1835   $171.18   $171.20   $171.20  
  7 purchase totals = $938.90       $996.8452   $996.83   $996.80   $996.90