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	$48.85	9.232%	$53.3598	$53.36	$53.35	$53.40
Purchase #2	$228.98	11.620%	$255.5875	$255.59	$255.60	$255.60
Purchase #3	$57.92	5.399%	$61.0471	$61.05	$61.05	$61.00
Purchase #4	$47.35	12.609%	$53.3204	$53.32	$53.30	$53.30
Purchase #5	$120.68	7.275%	$129.4595	$129.46	$129.45	$129.50
Purchase #6	$85.43	12.571%	$96.1694	$96.17	$96.15	$96.20
Purchase #7	$154.32	9.664%	$169.2335	$169.23	$169.25	$169.20
7 purchase totals =	$743.53		$818.1772	$818.18	$818.15	$818.20