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	$145.66	5.498%	$153.6684	$153.67	$153.65	$153.70
Purchase #2	$58.93	6.487%	$62.7528	$62.75	$62.75	$62.80
Purchase #3	$124.34	5.817%	$131.5729	$131.57	$131.55	$131.60
Purchase #4	$96.38	9.787%	$105.8127	$105.81	$105.80	$105.80
Purchase #5	$220.44	10.306%	$243.1585	$243.16	$243.15	$243.20
Purchase #6	$78.27	6.176%	$83.104	$83.10	$83.10	$83.10
Purchase #7	$20.78	4.450%	$21.7047	$21.70	$21.70	$21.70
7 purchase totals =	$744.80		$801.7740	$801.76	$801.70	$801.90