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	$98.28	6.337%	$104.508	$104.51	$104.50	$104.50
Purchase #2	$39.67	6.326%	$42.1795	$42.18	$42.20	$42.20
Purchase #3	$133.62	9.188%	$145.897	$145.90	$145.90	$145.90
Purchase #4	$86.82	5.659%	$91.7331	$91.73	$91.75	$91.70
Purchase #5	$55.51	11.383%	$61.8287	$61.83	$61.85	$61.80
Purchase #6	$121.91	6.381%	$129.6891	$129.69	$129.70	$129.70
Purchase #7	$221.86	9.805%	$243.6134	$243.61	$243.60	$243.60
7 purchase totals =	$757.67		$819.4488	$819.45	$819.50	$819.40