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	$245.79	6.522%	$261.8204	$261.82	$261.80	$261.80
Purchase #2	$147.93	12.398%	$166.2704	$166.27	$166.25	$166.30
Purchase #3	$130.68	8.873%	$142.2752	$142.28	$142.30	$142.30
Purchase #4	$244.53	12.596%	$275.331	$275.33	$275.35	$275.30
Purchase #5	$145.26	8.276%	$157.2817	$157.28	$157.30	$157.30
Purchase #6	$42.91	12.250%	$48.1665	$48.17	$48.15	$48.20
Purchase #7	$219.80	13.423%	$249.3038	$249.30	$249.30	$249.30
7 purchase totals =	$1,176.90		$1,300.4490	$1,300.45	$1,300.45	$1,300.50