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	$28.31	10.446%	$31.2673	$31.27	$31.25	$31.30
Purchase #2	$224.94	8.714%	$244.5413	$244.54	$244.55	$244.50
Purchase #3	$199.26	10.559%	$220.2999	$220.30	$220.30	$220.30
Purchase #4	$81.79	10.603%	$90.4622	$90.46	$90.45	$90.50
Purchase #5	$22.43	7.673%	$24.1511	$24.15	$24.15	$24.20
Purchase #6	$111.32	11.339%	$123.9426	$123.94	$123.95	$123.90
Purchase #7	$55.57	9.263%	$60.7174	$60.72	$60.70	$60.70
7 purchase totals =	$723.62		$795.3818	$795.38	$795.35	$795.40