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	$121.43	5.818%	$128.4948	$128.49	$128.50	$128.50
Purchase #2	$64.79	3.847%	$67.2825	$67.28	$67.30	$67.30
Purchase #3	$72.57	11.127%	$80.6449	$80.64	$80.65	$80.60
Purchase #4	$244.25	6.109%	$259.1712	$259.17	$259.15	$259.20
Purchase #5	$199.86	6.305%	$212.4612	$212.46	$212.45	$212.50
Purchase #6	$150.86	4.321%	$157.3787	$157.38	$157.40	$157.40
Purchase #7	$233.88	3.338%	$241.6869	$241.69	$241.70	$241.70
7 purchase totals =	$1,087.64		$1,147.1202	$1,147.11	$1,147.15	$1,147.20