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	$104.51	13.362%	$118.4746	$118.47	$118.45	$118.50
Purchase #2	$92.87	3.642%	$96.2523	$96.25	$96.25	$96.30
Purchase #3	$190.39	3.219%	$196.5187	$196.52	$196.50	$196.50
Purchase #4	$55.37	10.246%	$61.0432	$61.04	$61.05	$61.00
Purchase #5	$136.64	3.394%	$141.2776	$141.28	$141.30	$141.30
Purchase #6	$135.43	7.735%	$145.9055	$145.91	$145.90	$145.90
Purchase #7	$247.44	9.562%	$271.1002	$271.10	$271.10	$271.10
7 purchase totals =	$962.65		$1,030.5721	$1,030.57	$1,030.55	$1,030.60