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	$20.37	3.294%	$21.041	$21.04	$21.05	$21.00
Purchase #2	$96.40	10.495%	$106.5172	$106.52	$106.50	$106.50
Purchase #3	$6.53	9.423%	$7.1453	$7.15	$7.15	$7.10
Purchase #4	$229.58	3.339%	$237.2457	$237.25	$237.25	$237.20
Purchase #5	$175.37	9.706%	$192.3914	$192.39	$192.40	$192.40
Purchase #6	$226.98	10.501%	$250.8152	$250.82	$250.80	$250.80
Purchase #7	$131.43	11.738%	$146.8573	$146.86	$146.85	$146.90
7 purchase totals =	$886.66		$962.0131	$962.03	$962.00	$961.90