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	$166.59	11.203%	$185.2531	$185.25	$185.25	$185.30
Purchase #2	$159.85	6.739%	$170.6223	$170.62	$170.60	$170.60
Purchase #3	$125.27	8.392%	$135.7827	$135.78	$135.80	$135.80
Purchase #4	$101.95	9.231%	$111.361	$111.36	$111.35	$111.40
Purchase #5	$83.96	7.462%	$90.2251	$90.23	$90.25	$90.20
Purchase #6	$135.54	8.777%	$147.4363	$147.44	$147.45	$147.40
Purchase #7	$82.91	7.430%	$89.0702	$89.07	$89.05	$89.10
7 purchase totals =	$856.07		$929.7507	$929.75	$929.75	$929.80