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 $164.69   11.756%   $184.051   $184.05   $184.05   $184.10  
  Purchase #2 $35.48   12.266%   $39.832   $39.83   $39.85   $39.80  
  Purchase #3 $120.47   11.551%   $134.3855   $134.39   $134.40   $134.40  
  Purchase #4 $151.40   10.522%   $167.3303   $167.33   $167.35   $167.30  
  Purchase #5 $248.60   9.318%   $271.7645   $271.76   $271.75   $271.80  
  Purchase #6 $93.59   4.827%   $98.1076   $98.11   $98.10   $98.10  
  Purchase #7 $220.44   9.191%   $240.7006   $240.70   $240.70   $240.70  
  7 purchase totals = $1,034.67       $1,136.1715   $1,136.17   $1,136.20   $1,136.20