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	$42.52	7.791%	$45.8327	$45.83	$45.85	$45.80
Purchase #2	$90.42	9.738%	$99.2251	$99.23	$99.25	$99.20
Purchase #3	$51.78	13.402%	$58.7196	$58.72	$58.70	$58.70
Purchase #4	$211.42	4.195%	$220.2891	$220.29	$220.30	$220.30
Purchase #5	$51.50	5.718%	$54.4448	$54.44	$54.45	$54.40
Purchase #6	$229.74	3.700%	$238.2404	$238.24	$238.25	$238.20
Purchase #7	$31.89	7.290%	$34.2148	$34.21	$34.20	$34.20
7 purchase totals =	$709.27		$750.9665	$750.96	$751.00	$750.80