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	$159.85	13.768%	$181.8581	$181.86	$181.85	$181.90
Purchase #2	$139.95	4.360%	$146.0518	$146.05	$146.05	$146.10
Purchase #3	$141.41	3.125%	$145.8291	$145.83	$145.85	$145.80
Purchase #4	$54.53	11.328%	$60.7072	$60.71	$60.70	$60.70
Purchase #5	$55.82	6.215%	$59.2892	$59.29	$59.30	$59.30
Purchase #6	$73.29	13.494%	$83.1798	$83.18	$83.20	$83.20
Purchase #7	$67.76	7.805%	$73.0487	$73.05	$73.05	$73.00
7 purchase totals =	$692.61		$749.9639	$749.97	$750.00	$750.00