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	$18.83	13.226%	$21.3205	$21.32	$21.30	$21.30
Purchase #2	$74.33	9.385%	$81.3059	$81.31	$81.30	$81.30
Purchase #3	$42.84	6.834%	$45.7677	$45.77	$45.75	$45.80
Purchase #4	$235.55	12.457%	$264.8925	$264.89	$264.90	$264.90
Purchase #5	$127.36	9.620%	$139.612	$139.61	$139.60	$139.60
Purchase #6	$126.61	4.596%	$132.429	$132.43	$132.45	$132.40
Purchase #7	$239.62	10.506%	$264.7945	$264.79	$264.80	$264.80
7 purchase totals =	$865.14		$950.1221	$950.12	$950.10	$950.10