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	$107.64	10.834%	$119.3017	$119.30	$119.30	$119.30
Purchase #2	$82.32	10.232%	$90.743	$90.74	$90.75	$90.70
Purchase #3	$64.69	11.401%	$72.0653	$72.07	$72.05	$72.10
Purchase #4	$42.70	7.470%	$45.8897	$45.89	$45.90	$45.90
Purchase #5	$94.48	10.640%	$104.5327	$104.53	$104.55	$104.50
Purchase #6	$54.41	4.310%	$56.7551	$56.76	$56.75	$56.80
Purchase #7	$98.55	5.638%	$104.1062	$104.11	$104.10	$104.10
7 purchase totals =	$544.79		$593.3937	$593.40	$593.40	$593.40