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	$82.33	8.440%	$89.2787	$89.28	$89.30	$89.30
Purchase #2	$125.43	4.706%	$131.3327	$131.33	$131.35	$131.30
Purchase #3	$144.71	9.113%	$157.8974	$157.90	$157.90	$157.90
Purchase #4	$84.83	11.414%	$94.5125	$94.51	$94.50	$94.50
Purchase #5	$106.87	5.793%	$113.061	$113.06	$113.05	$113.10
Purchase #6	$129.65	5.864%	$137.2527	$137.25	$137.25	$137.30
Purchase #7	$117.40	8.234%	$127.0667	$127.07	$127.05	$127.10
7 purchase totals =	$791.22		$850.4017	$850.40	$850.40	$850.50