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	$165.50	11.608%	$184.7112	$184.71	$184.70	$184.70
Purchase #2	$79.82	3.199%	$82.3734	$82.37	$82.35	$82.40
Purchase #3	$29.54	9.405%	$32.3182	$32.32	$32.30	$32.30
Purchase #4	$35.55	13.734%	$40.4324	$40.43	$40.45	$40.40
Purchase #5	$37.50	4.301%	$39.1129	$39.11	$39.10	$39.10
Purchase #6	$114.51	5.508%	$120.8172	$120.82	$120.80	$120.80
Purchase #7	$168.27	10.739%	$186.3405	$186.34	$186.35	$186.30
7 purchase totals =	$630.69		$686.1058	$686.10	$686.05	$686.00