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	$140.70	7.443%	$151.1723	$151.17	$151.15	$151.20
Purchase #2	$36.89	3.260%	$38.0926	$38.09	$38.10	$38.10
Purchase #3	$18.84	8.824%	$20.5024	$20.50	$20.50	$20.50
Purchase #4	$101.80	9.399%	$111.3682	$111.37	$111.35	$111.40
Purchase #5	$234.82	6.511%	$250.1091	$250.11	$250.10	$250.10
Purchase #6	$235.73	9.806%	$258.8457	$258.85	$258.85	$258.80
Purchase #7	$228.30	9.476%	$249.9337	$249.93	$249.95	$249.90
7 purchase totals =	$997.08		$1,080.0240	$1,080.02	$1,080.00	$1,080.00