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	$33.49	11.399%	$37.3075	$37.31	$37.30	$37.30
Purchase #2	$112.83	4.168%	$117.5328	$117.53	$117.55	$117.50
Purchase #3	$35.33	8.783%	$38.433	$38.43	$38.45	$38.40
Purchase #4	$66.79	9.758%	$73.3074	$73.31	$73.30	$73.30
Purchase #5	$36.52	10.296%	$40.2801	$40.28	$40.30	$40.30
Purchase #6	$189.46	7.758%	$204.1583	$204.16	$204.15	$204.20
Purchase #7	$227.86	12.747%	$256.9053	$256.91	$256.90	$256.90
7 purchase totals =	$702.28		$767.9244	$767.93	$767.95	$767.90