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	$138.98	5.650%	$146.8324	$146.83	$146.85	$146.80
Purchase #2	$47.99	12.106%	$53.7997	$53.80	$53.80	$53.80
Purchase #3	$166.41	11.364%	$185.3208	$185.32	$185.30	$185.30
Purchase #4	$79.33	6.335%	$84.3556	$84.36	$84.35	$84.40
Purchase #5	$90.28	9.796%	$99.1238	$99.12	$99.10	$99.10
Purchase #6	$200.66	10.664%	$222.0584	$222.06	$222.05	$222.10
Purchase #7	$14.90	4.220%	$15.5288	$15.53	$15.55	$15.50
7 purchase totals =	$738.55		$807.0195	$807.02	$807.00	$807.00