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	$162.78	4.642%	$170.3362	$170.34	$170.35	$170.30
Purchase #2	$134.47	4.276%	$140.2199	$140.22	$140.20	$140.20
Purchase #3	$103.40	7.738%	$111.4011	$111.40	$111.40	$111.40
Purchase #4	$126.44	13.394%	$143.3754	$143.38	$143.40	$143.40
Purchase #5	$171.69	4.410%	$179.2615	$179.26	$179.25	$179.30
Purchase #6	$229.53	5.613%	$242.4135	$242.41	$242.40	$242.40
Purchase #7	$29.56	3.654%	$30.6401	$30.64	$30.65	$30.60
7 purchase totals =	$957.87		$1,017.6477	$1,017.65	$1,017.65	$1,017.60