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	$72.57	4.102%	$75.5468	$75.55	$75.55	$75.50
Purchase #2	$227.92	11.664%	$254.5046	$254.50	$254.50	$254.50
Purchase #3	$47.61	6.694%	$50.797	$50.80	$50.80	$50.80
Purchase #4	$233.41	9.536%	$255.668	$255.67	$255.65	$255.70
Purchase #5	$146.69	12.316%	$164.7563	$164.76	$164.75	$164.80
Purchase #6	$81.56	10.346%	$89.9982	$90.00	$90.00	$90.00
Purchase #7	$181.30	3.715%	$188.0353	$188.04	$188.05	$188.00
7 purchase totals =	$991.06		$1,079.3062	$1,079.32	$1,079.30	$1,079.30