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	$223.61	5.140%	$235.1036	$235.10	$235.10	$235.10
Purchase #2	$197.54	3.398%	$204.2524	$204.25	$204.25	$204.30
Purchase #3	$75.33	6.112%	$79.9342	$79.93	$79.95	$79.90
Purchase #4	$116.37	9.790%	$127.7626	$127.76	$127.75	$127.80
Purchase #5	$131.31	4.157%	$136.7686	$136.77	$136.75	$136.80
Purchase #6	$182.65	5.630%	$192.9332	$192.93	$192.95	$192.90
Purchase #7	$86.32	4.422%	$90.1371	$90.14	$90.15	$90.10
7 purchase totals =	$1,013.13		$1,066.8917	$1,066.88	$1,066.90	$1,066.90