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	$243.30	4.348%	$253.8787	$253.88	$253.90	$253.90
Purchase #2	$114.59	5.350%	$120.7206	$120.72	$120.70	$120.70
Purchase #3	$207.27	9.524%	$227.0104	$227.01	$227.00	$227.00
Purchase #4	$153.51	12.522%	$172.7325	$172.73	$172.75	$172.70
Purchase #5	$223.88	12.152%	$251.0859	$251.09	$251.10	$251.10
Purchase #6	$89.65	10.816%	$99.3465	$99.35	$99.35	$99.30
Purchase #7	$173.91	12.869%	$196.2905	$196.29	$196.30	$196.30
7 purchase totals =	$1,206.11		$1,321.0651	$1,321.07	$1,321.10	$1,321.00