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 $54.33   4.428%   $56.7357   $56.74   $56.75   $56.70  
  Purchase #2 $162.43   5.424%   $171.2402   $171.24   $171.25   $171.20  
  Purchase #3 $119.72   5.859%   $126.7344   $126.73   $126.75   $126.70  
  Purchase #4 $178.64   7.706%   $192.406   $192.41   $192.40   $192.40  
  Purchase #5 $196.82   11.342%   $219.1433   $219.14   $219.15   $219.10  
  Purchase #6 $236.30   6.874%   $252.5433   $252.54   $252.55   $252.50  
  Purchase #7 $103.29   13.343%   $117.072   $117.07   $117.05   $117.10  
  7 purchase totals = $1,051.53       $1,135.8749   $1,135.87   $1,135.90   $1,135.70