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	$26.25	3.467%	$27.1601	$27.16	$27.15	$27.20
Purchase #2	$50.43	8.829%	$54.8825	$54.88	$54.90	$54.90
Purchase #3	$173.75	7.494%	$186.7708	$186.77	$186.75	$186.80
Purchase #4	$237.83	3.806%	$246.8818	$246.88	$246.90	$246.90
Purchase #5	$222.31	4.294%	$231.856	$231.86	$231.85	$231.90
Purchase #6	$33.40	7.296%	$35.8369	$35.84	$35.85	$35.80
Purchase #7	$41.80	6.399%	$44.4748	$44.47	$44.45	$44.50
7 purchase totals =	$785.77		$827.8629	$827.86	$827.85	$828.00