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	$229.37	5.209%	$241.3179	$241.32	$241.30	$241.30
Purchase #2	$31.29	5.140%	$32.8983	$32.90	$32.90	$32.90
Purchase #3	$96.27	7.747%	$103.728	$103.73	$103.75	$103.70
Purchase #4	$198.88	11.593%	$221.9362	$221.94	$221.95	$221.90
Purchase #5	$207.70	6.664%	$221.5411	$221.54	$221.55	$221.50
Purchase #6	$238.93	13.712%	$271.6921	$271.69	$271.70	$271.70
Purchase #7	$122.90	5.399%	$129.5354	$129.54	$129.55	$129.50
7 purchase totals =	$1,125.34		$1,222.6490	$1,222.66	$1,222.70	$1,222.50