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	$17.35	4.505%	$18.1316	$18.13	$18.15	$18.10
Purchase #2	$38.49	5.385%	$40.5627	$40.56	$40.55	$40.60
Purchase #3	$98.74	6.406%	$105.0653	$105.07	$105.05	$105.10
Purchase #4	$170.47	9.289%	$186.305	$186.31	$186.30	$186.30
Purchase #5	$48.76	11.415%	$54.326	$54.33	$54.35	$54.30
Purchase #6	$171.53	8.369%	$185.8853	$185.89	$185.90	$185.90
Purchase #7	$171.39	13.327%	$194.2311	$194.23	$194.25	$194.20
7 purchase totals =	$716.73		$784.5070	$784.52	$784.55	$784.50