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	$72.37	11.690%	$80.8301	$80.83	$80.85	$80.80
Purchase #2	$94.74	4.750%	$99.2402	$99.24	$99.25	$99.20
Purchase #3	$223.80	13.411%	$253.8138	$253.81	$253.80	$253.80
Purchase #4	$31.99	4.191%	$33.3307	$33.33	$33.35	$33.30
Purchase #5	$130.39	7.241%	$139.8315	$139.83	$139.85	$139.80
Purchase #6	$159.72	8.102%	$172.6605	$172.66	$172.65	$172.70
Purchase #7	$228.66	12.368%	$256.9407	$256.94	$256.95	$256.90
7 purchase totals =	$941.67		$1,036.6475	$1,036.64	$1,036.70	$1,036.50