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	$102.73	7.233%	$110.1605	$110.16	$110.15	$110.20
Purchase #2	$228.64	6.665%	$243.8789	$243.88	$243.90	$243.90
Purchase #3	$134.76	5.260%	$141.8484	$141.85	$141.85	$141.80
Purchase #4	$216.96	7.636%	$233.5271	$233.53	$233.55	$233.50
Purchase #5	$119.44	10.502%	$131.9836	$131.98	$132.00	$132.00
Purchase #6	$89.92	8.447%	$97.5155	$97.52	$97.50	$97.50
Purchase #7	$31.45	10.145%	$34.6406	$34.64	$34.65	$34.60
7 purchase totals =	$923.90		$993.5546	$993.56	$993.60	$993.50