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	$128.53	12.270%	$144.3006	$144.30	$144.30	$144.30
Purchase #2	$139.80	13.498%	$158.6702	$158.67	$158.65	$158.70
Purchase #3	$95.31	11.198%	$105.9828	$105.98	$106.00	$106.00
Purchase #4	$248.85	10.820%	$275.7756	$275.78	$275.80	$275.80
Purchase #5	$11.88	12.711%	$13.3901	$13.39	$13.40	$13.40
Purchase #6	$188.29	3.155%	$194.2305	$194.23	$194.25	$194.20
Purchase #7	$245.39	3.195%	$253.2302	$253.23	$253.25	$253.20
7 purchase totals =	$1,058.05		$1,145.5800	$1,145.58	$1,145.65	$1,145.60