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 $208.60   12.459%   $234.5895   $234.59   $234.60   $234.60  
  Purchase #2 $239.61   3.593%   $248.2192   $248.22   $248.20   $248.20  
  Purchase #3 $243.96   5.855%   $258.2439   $258.24   $258.25   $258.20  
  Purchase #4 $70.33   8.409%   $76.244   $76.24   $76.25   $76.20  
  Purchase #5 $231.51   5.721%   $244.7547   $244.75   $244.75   $244.80  
  Purchase #6 $179.86   8.267%   $194.729   $194.73   $194.75   $194.70  
  Purchase #7 $250.85   7.357%   $269.305   $269.31   $269.30   $269.30  
  7 purchase totals = $1,424.72       $1,526.0853   $1,526.08   $1,526.10   $1,526.00