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	$139.36	6.172%	$147.9613	$147.96	$147.95	$148.00
Purchase #2	$247.28	12.666%	$278.6005	$278.60	$278.60	$278.60
Purchase #3	$50.58	10.473%	$55.8772	$55.88	$55.90	$55.90
Purchase #4	$249.25	11.644%	$278.2727	$278.27	$278.25	$278.30
Purchase #5	$40.54	3.333%	$41.8912	$41.89	$41.90	$41.90
Purchase #6	$58.82	4.188%	$61.2834	$61.28	$61.30	$61.30
Purchase #7	$12.83	7.237%	$13.7585	$13.76	$13.75	$13.80
7 purchase totals =	$798.66		$877.6448	$877.64	$877.65	$877.80