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	$40.74	11.151%	$45.2829	$45.28	$45.30	$45.30
Purchase #2	$68.55	12.853%	$77.3607	$77.36	$77.35	$77.40
Purchase #3	$217.34	9.237%	$237.4157	$237.42	$237.40	$237.40
Purchase #4	$59.76	6.413%	$63.5924	$63.59	$63.60	$63.60
Purchase #5	$27.29	11.703%	$30.4837	$30.48	$30.50	$30.50
Purchase #6	$39.56	8.733%	$43.0148	$43.01	$43.00	$43.00
Purchase #7	$85.89	3.630%	$89.0078	$89.01	$89.00	$89.00
7 purchase totals =	$539.13		$586.1580	$586.15	$586.15	$586.20