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	$50.82	5.769%	$53.7518	$53.75	$53.75	$53.80
Purchase #2	$130.30	8.760%	$141.7143	$141.71	$141.70	$141.70
Purchase #3	$72.26	11.131%	$80.3033	$80.30	$80.30	$80.30
Purchase #4	$64.81	12.321%	$72.7952	$72.80	$72.80	$72.80
Purchase #5	$230.27	12.231%	$258.4343	$258.43	$258.45	$258.40
Purchase #6	$18.27	4.665%	$19.1223	$19.12	$19.10	$19.10
Purchase #7	$35.76	13.717%	$40.6652	$40.67	$40.65	$40.70
7 purchase totals =	$602.49		$666.7864	$666.78	$666.75	$666.80