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	$234.67	3.769%	$243.5147	$243.51	$243.50	$243.50
Purchase #2	$57.65	6.134%	$61.1863	$61.19	$61.20	$61.20
Purchase #3	$185.59	12.501%	$208.7906	$208.79	$208.80	$208.80
Purchase #4	$21.59	8.392%	$23.4018	$23.40	$23.40	$23.40
Purchase #5	$173.74	4.122%	$180.9016	$180.90	$180.90	$180.90
Purchase #6	$100.46	10.867%	$111.377	$111.38	$111.40	$111.40
Purchase #7	$230.67	12.502%	$259.5084	$259.51	$259.50	$259.50
7 purchase totals =	$1,004.37		$1,088.6804	$1,088.68	$1,088.70	$1,088.70