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	$73.90	12.314%	$83	$83.00	$83.00	$83.00
Purchase #2	$229.71	11.566%	$256.2783	$256.28	$256.30	$256.30
Purchase #3	$89.72	8.399%	$97.2556	$97.26	$97.25	$97.30
Purchase #4	$29.67	4.640%	$31.0467	$31.05	$31.05	$31.00
Purchase #5	$222.49	3.698%	$230.7177	$230.72	$230.70	$230.70
Purchase #6	$222.48	3.786%	$230.9031	$230.90	$230.90	$230.90
Purchase #7	$167.75	10.743%	$185.7714	$185.77	$185.75	$185.80
7 purchase totals =	$1,035.72		$1,114.9728	$1,114.98	$1,114.95	$1,115.00