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	$45.60	11.546%	$50.865	$50.87	$50.85	$50.90
Purchase #2	$72.79	13.306%	$82.4754	$82.48	$82.50	$82.50
Purchase #3	$62.87	7.670%	$67.6921	$67.69	$67.70	$67.70
Purchase #4	$210.31	12.368%	$236.3211	$236.32	$236.30	$236.30
Purchase #5	$195.62	13.355%	$221.7451	$221.75	$221.75	$221.70
Purchase #6	$194.96	11.539%	$217.4564	$217.46	$217.45	$217.50
Purchase #7	$72.45	8.664%	$78.7271	$78.73	$78.75	$78.70
7 purchase totals =	$854.60		$955.2822	$955.30	$955.30	$955.30