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 $38.35   13.704%   $43.6055   $43.61   $43.60   $43.60  
  Purchase #2 $215.51   8.186%   $233.1516   $233.15   $233.15   $233.20  
  Purchase #3 $102.49   7.240%   $109.9103   $109.91   $109.90   $109.90  
  Purchase #4 $244.49   11.251%   $271.9976   $272.00   $272.00   $272.00  
  Purchase #5 $80.63   6.413%   $85.8008   $85.80   $85.80   $85.80  
  Purchase #6 $192.72   9.463%   $210.9571   $210.96   $210.95   $211.00  
  Purchase #7 $32.62   7.408%   $35.0365   $35.04   $35.05   $35.00  
  7 purchase totals = $906.81       $990.4594   $990.47   $990.45   $990.50