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	$151.51	6.198%	$160.9006	$160.90	$160.90	$160.90
Purchase #2	$179.54	6.138%	$190.5602	$190.56	$190.55	$190.60
Purchase #3	$232.62	13.567%	$264.1796	$264.18	$264.20	$264.20
Purchase #4	$62.76	6.490%	$66.8331	$66.83	$66.85	$66.80
Purchase #5	$245.32	13.850%	$279.2968	$279.30	$279.30	$279.30
Purchase #6	$196.67	12.420%	$221.0964	$221.10	$221.10	$221.10
Purchase #7	$190.41	7.195%	$204.11	$204.11	$204.10	$204.10
7 purchase totals =	$1,258.83		$1,386.9767	$1,386.98	$1,387.00	$1,387.00