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	$233.29	9.567%	$255.6089	$255.61	$255.60	$255.60
Purchase #2	$39.33	12.625%	$44.2954	$44.30	$44.30	$44.30
Purchase #3	$211.27	4.297%	$220.3483	$220.35	$220.35	$220.30
Purchase #4	$99.31	3.600%	$102.8852	$102.89	$102.90	$102.90
Purchase #5	$28.81	8.783%	$31.3404	$31.34	$31.35	$31.30
Purchase #6	$244.81	12.578%	$275.6022	$275.60	$275.60	$275.60
Purchase #7	$49.34	6.650%	$52.6211	$52.62	$52.60	$52.60
7 purchase totals =	$906.16		$982.7015	$982.71	$982.70	$982.60