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	$47.59	5.111%	$50.0223	$50.02	$50.00	$50.00
Purchase #2	$56.55	5.697%	$59.7717	$59.77	$59.75	$59.80
Purchase #3	$70.48	11.465%	$78.5605	$78.56	$78.55	$78.60
Purchase #4	$107.39	12.247%	$120.5421	$120.54	$120.55	$120.50
Purchase #5	$191.99	10.474%	$212.099	$212.10	$212.10	$212.10
Purchase #6	$221.59	12.650%	$249.6211	$249.62	$249.60	$249.60
Purchase #7	$127.37	13.621%	$144.7191	$144.72	$144.70	$144.70
7 purchase totals =	$822.96		$915.3358	$915.33	$915.25	$915.30