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	$229.77	12.418%	$258.3028	$258.30	$258.30	$258.30
Purchase #2	$37.26	7.822%	$40.1745	$40.17	$40.15	$40.20
Purchase #3	$89.79	11.403%	$100.0288	$100.03	$100.05	$100.00
Purchase #4	$237.61	9.531%	$260.2566	$260.26	$260.25	$260.30
Purchase #5	$232.82	12.148%	$261.103	$261.10	$261.10	$261.10
Purchase #6	$76.40	12.153%	$85.6849	$85.68	$85.70	$85.70
Purchase #7	$62.38	4.801%	$65.3749	$65.37	$65.35	$65.40
7 purchase totals =	$966.03		$1,070.9255	$1,070.91	$1,070.90	$1,071.00