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	$138.70	3.420%	$143.4435	$143.44	$143.45	$143.40
Purchase #2	$192.73	3.104%	$198.7123	$198.71	$198.70	$198.70
Purchase #3	$171.30	7.574%	$184.2743	$184.27	$184.25	$184.30
Purchase #4	$108.51	13.372%	$123.02	$123.02	$123.00	$123.00
Purchase #5	$221.59	3.468%	$229.2747	$229.27	$229.25	$229.30
Purchase #6	$189.77	3.462%	$196.3398	$196.34	$196.35	$196.30
Purchase #7	$124.67	9.347%	$136.3229	$136.32	$136.30	$136.30
7 purchase totals =	$1,147.27		$1,211.3875	$1,211.37	$1,211.30	$1,211.30