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 $148.81   11.728%   $166.2624   $166.26   $166.25   $166.30  
  Purchase #2 $177.71   6.114%   $188.5752   $188.58   $188.60   $188.60  
  Purchase #3 $216.77   3.277%   $223.8736   $223.87   $223.85   $223.90  
  Purchase #4 $162.77   7.319%   $174.6831   $174.68   $174.70   $174.70  
  Purchase #5 $32.75   10.266%   $36.1121   $36.11   $36.10   $36.10  
  Purchase #6 $227.52   13.607%   $258.4786   $258.48   $258.50   $258.50  
  Purchase #7 $18.58   7.203%   $19.9183   $19.92   $19.90   $19.90  
  7 purchase totals = $984.91       $1,067.9033   $1,067.90   $1,067.90   $1,068.00