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	$137.82	4.870%	$144.5318	$144.53	$144.55	$144.50
Purchase #2	$159.54	12.604%	$179.6484	$179.65	$179.65	$179.60
Purchase #3	$177.29	7.721%	$190.9786	$190.98	$191.00	$191.00
Purchase #4	$151.64	7.436%	$162.916	$162.92	$162.90	$162.90
Purchase #5	$243.58	12.621%	$274.3222	$274.32	$274.30	$274.30
Purchase #6	$221.95	9.414%	$242.8444	$242.84	$242.85	$242.80
Purchase #7	$67.51	13.429%	$76.5759	$76.58	$76.60	$76.60
7 purchase totals =	$1,159.33		$1,271.8173	$1,271.82	$1,271.85	$1,271.70