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	$29.46	13.257%	$33.3655	$33.37	$33.35	$33.40
Purchase #2	$125.41	4.184%	$130.6572	$130.66	$130.65	$130.70
Purchase #3	$81.97	10.429%	$90.5187	$90.52	$90.50	$90.50
Purchase #4	$243.85	9.120%	$266.0891	$266.09	$266.10	$266.10
Purchase #5	$246.58	3.869%	$256.1202	$256.12	$256.10	$256.10
Purchase #6	$128.61	6.660%	$137.1754	$137.18	$137.20	$137.20
Purchase #7	$221.88	7.709%	$238.9847	$238.98	$239.00	$239.00
7 purchase totals =	$1,077.76		$1,152.9108	$1,152.92	$1,152.90	$1,153.00