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	$74.87	3.872%	$77.769	$77.77	$77.75	$77.80
Purchase #2	$209.82	7.186%	$224.8977	$224.90	$224.90	$224.90
Purchase #3	$56.36	10.216%	$62.1177	$62.12	$62.10	$62.10
Purchase #4	$73.95	6.143%	$78.4927	$78.49	$78.50	$78.50
Purchase #5	$53.98	13.713%	$61.3823	$61.38	$61.40	$61.40
Purchase #6	$155.92	9.205%	$170.2724	$170.27	$170.25	$170.30
Purchase #7	$61.91	5.531%	$65.3342	$65.33	$65.35	$65.30
7 purchase totals =	$686.81		$740.2660	$740.26	$740.25	$740.30