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	$129.64	5.850%	$137.2239	$137.22	$137.20	$137.20
Purchase #2	$142.44	9.867%	$156.4946	$156.49	$156.50	$156.50
Purchase #3	$250.34	10.447%	$276.493	$276.49	$276.50	$276.50
Purchase #4	$67.85	6.682%	$72.3837	$72.38	$72.40	$72.40
Purchase #5	$26.30	6.320%	$27.9622	$27.96	$27.95	$28.00
Purchase #6	$192.82	9.502%	$211.1418	$211.14	$211.15	$211.10
Purchase #7	$179.62	5.524%	$189.5422	$189.54	$189.55	$189.50
7 purchase totals =	$989.01		$1,071.2414	$1,071.22	$1,071.25	$1,071.20