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 $248.84   5.425%   $262.3396   $262.34   $262.35   $262.30  
  Purchase #2 $215.72   9.251%   $235.6763   $235.68   $235.70   $235.70  
  Purchase #3 $223.41   13.235%   $252.9783   $252.98   $253.00   $253.00  
  Purchase #4 $46.93   3.610%   $48.6242   $48.62   $48.60   $48.60  
  Purchase #5 $131.52   3.222%   $135.7576   $135.76   $135.75   $135.80  
  Purchase #6 $225.97   13.129%   $255.6376   $255.64   $255.65   $255.60  
  Purchase #7 $73.79   3.789%   $76.5859   $76.59   $76.60   $76.60  
  7 purchase totals = $1,166.18       $1,267.5995   $1,267.61   $1,267.65   $1,267.60