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 $118.77   6.245%   $126.1872   $126.19   $126.20   $126.20  
  Purchase #2 $142.74   13.565%   $162.1027   $162.10   $162.10   $162.10  
  Purchase #3 $231.64   3.658%   $240.1134   $240.11   $240.10   $240.10  
  Purchase #4 $174.54   4.758%   $182.8446   $182.84   $182.85   $182.80  
  Purchase #5 $8.68   4.163%   $9.0413   $9.04   $9.05   $9.00  
  Purchase #6 $241.87   7.388%   $259.7394   $259.74   $259.75   $259.70  
  Purchase #7 $63.84   11.269%   $71.0341   $71.03   $71.05   $71.00  
  7 purchase totals = $982.08       $1,051.0627   $1,051.05   $1,051.10   $1,050.90