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	$53.80	9.863%	$59.1063	$59.11	$59.10	$59.10
Purchase #2	$138.30	6.213%	$146.8926	$146.89	$146.90	$146.90
Purchase #3	$117.91	13.532%	$133.8656	$133.87	$133.85	$133.90
Purchase #4	$211.80	3.362%	$218.9207	$218.92	$218.90	$218.90
Purchase #5	$108.39	7.612%	$116.6406	$116.64	$116.65	$116.60
Purchase #6	$197.42	7.319%	$211.8692	$211.87	$211.85	$211.90
Purchase #7	$197.43	3.453%	$204.2473	$204.25	$204.25	$204.20
7 purchase totals =	$1,025.05		$1,091.5423	$1,091.55	$1,091.50	$1,091.50