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	$55.31	11.681%	$61.7708	$61.77	$61.75	$61.80
Purchase #2	$100.69	5.133%	$105.8584	$105.86	$105.85	$105.90
Purchase #3	$198.71	13.657%	$225.8478	$225.85	$225.85	$225.80
Purchase #4	$96.68	8.850%	$105.2362	$105.24	$105.25	$105.20
Purchase #5	$24.74	6.165%	$26.2652	$26.27	$26.25	$26.30
Purchase #6	$79.72	11.250%	$88.6885	$88.69	$88.70	$88.70
Purchase #7	$222.86	3.453%	$230.5554	$230.56	$230.55	$230.60
7 purchase totals =	$778.71		$844.2223	$844.24	$844.20	$844.30