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	$82.78	7.737%	$89.1847	$89.18	$89.20	$89.20
Purchase #2	$228.50	5.755%	$241.6502	$241.65	$241.65	$241.70
Purchase #3	$53.33	10.769%	$59.0731	$59.07	$59.05	$59.10
Purchase #4	$80.26	12.525%	$90.3126	$90.31	$90.30	$90.30
Purchase #5	$77.57	11.864%	$86.7729	$86.77	$86.75	$86.80
Purchase #6	$19.53	8.679%	$21.225	$21.23	$21.25	$21.20
Purchase #7	$25.76	3.201%	$26.5846	$26.58	$26.60	$26.60
7 purchase totals =	$567.73		$614.8031	$614.79	$614.80	$614.90