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	$32.30	7.592%	$34.7522	$34.75	$34.75	$34.80
Purchase #2	$140.90	6.580%	$150.1712	$150.17	$150.15	$150.20
Purchase #3	$39.79	13.803%	$45.2822	$45.28	$45.30	$45.30
Purchase #4	$160.59	10.818%	$177.9626	$177.96	$177.95	$178.00
Purchase #5	$83.63	7.400%	$89.8186	$89.82	$89.80	$89.80
Purchase #6	$129.93	12.744%	$146.4883	$146.49	$146.50	$146.50
Purchase #7	$205.41	11.684%	$229.4101	$229.41	$229.40	$229.40
7 purchase totals =	$792.55		$873.8852	$873.88	$873.85	$874.00