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	$142.73	11.258%	$158.7985	$158.80	$158.80	$158.80
Purchase #2	$140.89	8.485%	$152.8445	$152.84	$152.85	$152.80
Purchase #3	$57.49	11.855%	$64.3054	$64.31	$64.30	$64.30
Purchase #4	$111.80	13.727%	$127.1468	$127.15	$127.15	$127.10
Purchase #5	$83.78	6.254%	$89.0196	$89.02	$89.00	$89.00
Purchase #6	$37.71	6.235%	$40.0612	$40.06	$40.05	$40.10
Purchase #7	$122.68	10.163%	$135.148	$135.15	$135.15	$135.10
7 purchase totals =	$697.08		$767.3240	$767.33	$767.30	$767.20