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 $169.94   5.873%   $179.9206   $179.92   $179.90   $179.90  
  Purchase #2 $143.66   13.364%   $162.8587   $162.86   $162.85   $162.90  
  Purchase #3 $196.64   6.239%   $208.9084   $208.91   $208.90   $208.90  
  Purchase #4 $157.76   5.386%   $166.257   $166.26   $166.25   $166.30  
  Purchase #5 $71.45   7.269%   $76.6437   $76.64   $76.65   $76.60  
  Purchase #6 $203.70   9.541%   $223.135   $223.14   $223.15   $223.10  
  Purchase #7 $48.99   10.227%   $54.0002   $54.00   $54.00   $54.00  
  7 purchase totals = $992.14       $1,071.7236   $1,071.73   $1,071.70   $1,071.70