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	$128.59	12.222%	$144.3063	$144.31	$144.30	$144.30
Purchase #2	$56.46	4.140%	$58.7974	$58.80	$58.80	$58.80
Purchase #3	$231.27	7.270%	$248.0833	$248.08	$248.10	$248.10
Purchase #4	$133.76	3.408%	$138.3185	$138.32	$138.30	$138.30
Purchase #5	$147.28	3.563%	$152.5276	$152.53	$152.55	$152.50
Purchase #6	$225.99	10.865%	$250.5438	$250.54	$250.55	$250.50
Purchase #7	$147.43	7.289%	$158.1762	$158.18	$158.20	$158.20
7 purchase totals =	$1,070.78		$1,150.7531	$1,150.76	$1,150.80	$1,150.70