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 $32.61   7.452%   $35.0401   $35.04   $35.05   $35.00  
  Purchase #2 $163.29   9.333%   $178.5299   $178.53   $178.55   $178.50  
  Purchase #3 $227.30   12.439%   $255.5738   $255.57   $255.55   $255.60  
  Purchase #4 $34.44   4.452%   $35.9733   $35.97   $35.95   $36.00  
  Purchase #5 $155.32   9.364%   $169.8642   $169.86   $169.85   $169.90  
  Purchase #6 $147.74   11.402%   $164.5853   $164.59   $164.60   $164.60  
  Purchase #7 $214.88   13.645%   $244.2004   $244.20   $244.20   $244.20  
  7 purchase totals = $975.58       $1,083.7670   $1,083.76   $1,083.75   $1,083.80