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	$39.42	7.834%	$42.5082	$42.51	$42.50	$42.50
Purchase #2	$22.28	12.744%	$25.1194	$25.12	$25.10	$25.10
Purchase #3	$94.69	11.683%	$105.7526	$105.75	$105.75	$105.80
Purchase #4	$234.75	5.195%	$246.9453	$246.95	$246.95	$246.90
Purchase #5	$33.44	11.825%	$37.3943	$37.39	$37.40	$37.40
Purchase #6	$40.75	11.135%	$45.2875	$45.29	$45.30	$45.30
Purchase #7	$184.53	6.789%	$197.0577	$197.06	$197.05	$197.10
7 purchase totals =	$649.86		$700.0650	$700.07	$700.05	$700.10