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	$34.89	8.594%	$37.8884	$37.89	$37.90	$37.90
Purchase #2	$116.49	13.233%	$131.9051	$131.91	$131.90	$131.90
Purchase #3	$213.52	4.795%	$223.7583	$223.76	$223.75	$223.80
Purchase #4	$192.81	8.705%	$209.5941	$209.59	$209.60	$209.60
Purchase #5	$71.53	3.394%	$73.9577	$73.96	$73.95	$74.00
Purchase #6	$47.27	5.725%	$49.9762	$49.98	$50.00	$50.00
Purchase #7	$239.79	4.242%	$249.9619	$249.96	$249.95	$250.00
7 purchase totals =	$916.30		$977.0417	$977.05	$977.05	$977.20