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	$233.80	11.848%	$261.5006	$261.50	$261.50	$261.50
Purchase #2	$215.85	13.478%	$244.9423	$244.94	$244.95	$244.90
Purchase #3	$186.37	12.622%	$209.8936	$209.89	$209.90	$209.90
Purchase #4	$227.98	7.114%	$244.1985	$244.20	$244.20	$244.20
Purchase #5	$43.38	9.190%	$47.3666	$47.37	$47.35	$47.40
Purchase #6	$64.78	12.112%	$72.6262	$72.63	$72.65	$72.60
Purchase #7	$77.26	6.306%	$82.132	$82.13	$82.15	$82.10
7 purchase totals =	$1,049.42		$1,162.6598	$1,162.66	$1,162.70	$1,162.60