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	$61.78	7.303%	$66.2918	$66.29	$66.30	$66.30
Purchase #2	$73.83	12.768%	$83.2566	$83.26	$83.25	$83.30
Purchase #3	$50.83	10.417%	$56.125	$56.13	$56.15	$56.10
Purchase #4	$63.76	11.410%	$71.035	$71.04	$71.05	$71.00
Purchase #5	$37.49	6.234%	$39.8271	$39.83	$39.85	$39.80
Purchase #6	$153.85	6.809%	$164.3256	$164.33	$164.35	$164.30
Purchase #7	$69.37	11.734%	$77.5099	$77.51	$77.50	$77.50
7 purchase totals =	$510.91		$558.3710	$558.39	$558.45	$558.30