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	$137.68	12.753%	$155.2383	$155.24	$155.25	$155.20
Purchase #2	$237.33	11.498%	$264.6182	$264.62	$264.60	$264.60
Purchase #3	$220.87	10.583%	$244.2447	$244.24	$244.25	$244.20
Purchase #4	$206.49	8.436%	$223.9095	$223.91	$223.90	$223.90
Purchase #5	$67.60	10.665%	$74.8095	$74.81	$74.80	$74.80
Purchase #6	$88.59	4.427%	$92.5119	$92.51	$92.50	$92.50
Purchase #7	$139.47	3.764%	$144.7197	$144.72	$144.70	$144.70
7 purchase totals =	$1,098.03		$1,200.0518	$1,200.05	$1,200.00	$1,199.90