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	$145.92	12.801%	$164.5992	$164.60	$164.60	$164.60
Purchase #2	$217.44	13.288%	$246.3334	$246.33	$246.35	$246.30
Purchase #3	$178.56	7.323%	$191.6359	$191.64	$191.65	$191.60
Purchase #4	$156.69	9.763%	$171.9876	$171.99	$172.00	$172.00
Purchase #5	$72.49	9.448%	$79.3389	$79.34	$79.35	$79.30
Purchase #6	$175.70	4.311%	$183.2744	$183.27	$183.25	$183.30
Purchase #7	$65.66	9.817%	$72.1058	$72.11	$72.10	$72.10
7 purchase totals =	$1,012.46		$1,109.2752	$1,109.28	$1,109.30	$1,109.20