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	$61.86	6.296%	$65.7547	$65.75	$65.75	$65.80
Purchase #2	$174.77	8.626%	$189.8457	$189.85	$189.85	$189.80
Purchase #3	$47.28	10.544%	$52.2652	$52.27	$52.25	$52.30
Purchase #4	$23.96	13.732%	$27.2502	$27.25	$27.25	$27.30
Purchase #5	$179.74	3.381%	$185.817	$185.82	$185.80	$185.80
Purchase #6	$14.29	11.261%	$15.8992	$15.90	$15.90	$15.90
Purchase #7	$93.49	5.275%	$98.4216	$98.42	$98.40	$98.40
7 purchase totals =	$595.39		$635.2536	$635.26	$635.20	$635.30