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	$79.36	12.828%	$89.5403	$89.54	$89.55	$89.50
Purchase #2	$165.43	5.585%	$174.6693	$174.67	$174.65	$174.70
Purchase #3	$176.70	7.301%	$189.6009	$189.60	$189.60	$189.60
Purchase #4	$197.39	13.372%	$223.785	$223.79	$223.80	$223.80
Purchase #5	$48.98	9.457%	$53.612	$53.61	$53.60	$53.60
Purchase #6	$214.96	10.557%	$237.6533	$237.65	$237.65	$237.70
Purchase #7	$28.80	10.170%	$31.729	$31.73	$31.75	$31.70
7 purchase totals =	$911.62		$1,000.5898	$1,000.59	$1,000.60	$1,000.60