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	$47.76	11.857%	$53.4229	$53.42	$53.40	$53.40
Purchase #2	$144.69	12.109%	$162.2105	$162.21	$162.20	$162.20
Purchase #3	$37.47	4.535%	$39.1693	$39.17	$39.15	$39.20
Purchase #4	$148.78	4.617%	$155.6492	$155.65	$155.65	$155.60
Purchase #5	$6.63	12.744%	$7.4749	$7.47	$7.45	$7.50
Purchase #6	$136.83	12.385%	$153.7764	$153.78	$153.80	$153.80
Purchase #7	$248.96	7.434%	$267.4677	$267.47	$267.45	$267.50
7 purchase totals =	$771.12		$839.1709	$839.17	$839.10	$839.20