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	$30.60	8.131%	$33.0881	$33.09	$33.10	$33.10
Purchase #2	$229.94	11.134%	$255.5415	$255.54	$255.55	$255.50
Purchase #3	$39.36	13.177%	$44.5465	$44.55	$44.55	$44.50
Purchase #4	$213.31	13.793%	$242.7318	$242.73	$242.75	$242.70
Purchase #5	$174.83	5.644%	$184.6974	$184.70	$184.70	$184.70
Purchase #6	$59.43	12.744%	$67.0038	$67.00	$67.00	$67.00
Purchase #7	$98.86	4.637%	$103.4441	$103.44	$103.45	$103.40
7 purchase totals =	$846.33		$931.0532	$931.05	$931.10	$930.90