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 $239.44   13.623%   $272.0589   $272.06   $272.05   $272.10  
  Purchase #2 $226.42   11.133%   $251.6273   $251.63   $251.65   $251.60  
  Purchase #3 $250.56   10.346%   $276.4829   $276.48   $276.50   $276.50  
  Purchase #4 $219.83   13.596%   $249.7181   $249.72   $249.70   $249.70  
  Purchase #5 $167.25   8.728%   $181.8476   $181.85   $181.85   $181.80  
  Purchase #6 $192.39   9.771%   $211.1884   $211.19   $211.20   $211.20  
  Purchase #7 $234.70   5.800%   $248.3126   $248.31   $248.30   $248.30  
  7 purchase totals = $1,530.59       $1,691.2358   $1,691.24   $1,691.25   $1,691.20