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	$15.88	3.456%	$16.4288	$16.43	$16.45	$16.40
Purchase #2	$219.87	8.457%	$238.4644	$238.46	$238.45	$238.50
Purchase #3	$85.90	4.216%	$89.5215	$89.52	$89.50	$89.50
Purchase #4	$123.76	4.280%	$129.0569	$129.06	$129.05	$129.10
Purchase #5	$7.75	3.795%	$8.0441	$8.04	$8.05	$8.00
Purchase #6	$157.89	12.818%	$178.1283	$178.13	$178.15	$178.10
Purchase #7	$127.90	3.104%	$131.87	$131.87	$131.85	$131.90
7 purchase totals =	$738.95		$791.5140	$791.51	$791.50	$791.50