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	$205.45	11.687%	$229.4609	$229.46	$229.45	$229.50
Purchase #2	$250.56	3.771%	$260.0086	$260.01	$260.00	$260.00
Purchase #3	$88.40	10.784%	$97.9331	$97.93	$97.95	$97.90
Purchase #4	$42.96	5.278%	$45.2274	$45.23	$45.25	$45.20
Purchase #5	$20.89	7.192%	$22.3924	$22.39	$22.40	$22.40
Purchase #6	$154.63	6.614%	$164.8572	$164.86	$164.85	$164.90
Purchase #7	$25.50	10.371%	$28.1446	$28.14	$28.15	$28.10
7 purchase totals =	$788.39		$848.0242	$848.02	$848.05	$848.00