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	$33.76	9.481%	$36.9608	$36.96	$36.95	$37.00
Purchase #2	$60.90	12.184%	$68.3201	$68.32	$68.30	$68.30
Purchase #3	$57.81	8.212%	$62.5574	$62.56	$62.55	$62.60
Purchase #4	$96.40	9.671%	$105.7228	$105.72	$105.70	$105.70
Purchase #5	$191.25	4.241%	$199.3609	$199.36	$199.35	$199.40
Purchase #6	$117.35	13.264%	$132.9153	$132.92	$132.90	$132.90
Purchase #7	$54.92	7.482%	$59.0291	$59.03	$59.05	$59.00
7 purchase totals =	$612.39		$664.8664	$664.87	$664.80	$664.90