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	$150.32	9.253%	$164.2291	$164.23	$164.25	$164.20
Purchase #2	$227.28	7.735%	$244.8601	$244.86	$244.85	$244.90
Purchase #3	$230.89	8.332%	$250.1278	$250.13	$250.15	$250.10
Purchase #4	$194.60	12.689%	$219.2928	$219.29	$219.30	$219.30
Purchase #5	$129.66	12.348%	$145.6704	$145.67	$145.65	$145.70
Purchase #6	$65.89	12.180%	$73.9154	$73.92	$73.90	$73.90
Purchase #7	$124.40	9.459%	$136.167	$136.17	$136.15	$136.20
7 purchase totals =	$1,123.04		$1,234.2626	$1,234.27	$1,234.25	$1,234.30