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	$248.56	8.632%	$270.0157	$270.02	$270.00	$270.00
Purchase #2	$223.91	11.313%	$249.2409	$249.24	$249.25	$249.20
Purchase #3	$243.57	4.624%	$254.8327	$254.83	$254.85	$254.80
Purchase #4	$19.57	10.229%	$21.5718	$21.57	$21.55	$21.60
Purchase #5	$109.70	6.541%	$116.8755	$116.88	$116.90	$116.90
Purchase #6	$105.25	12.163%	$118.0516	$118.05	$118.05	$118.10
Purchase #7	$18.42	4.710%	$19.2876	$19.29	$19.30	$19.30
7 purchase totals =	$968.98		$1,049.8758	$1,049.88	$1,049.90	$1,049.90