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	$186.28	6.580%	$198.5372	$198.54	$198.55	$198.50
Purchase #2	$91.81	8.227%	$99.3632	$99.36	$99.35	$99.40
Purchase #3	$90.87	8.355%	$98.4622	$98.46	$98.45	$98.50
Purchase #4	$49.65	7.594%	$53.4204	$53.42	$53.40	$53.40
Purchase #5	$214.45	7.190%	$229.869	$229.87	$229.85	$229.90
Purchase #6	$153.82	11.683%	$171.7908	$171.79	$171.80	$171.80
Purchase #7	$17.83	7.364%	$19.143	$19.14	$19.15	$19.10
7 purchase totals =	$804.71		$870.5858	$870.58	$870.55	$870.60