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	$64.42	8.689%	$70.0175	$70.02	$70.00	$70.00
Purchase #2	$191.85	7.836%	$206.8834	$206.88	$206.90	$206.90
Purchase #3	$26.34	6.557%	$28.0671	$28.07	$28.05	$28.10
Purchase #4	$112.40	3.681%	$116.5374	$116.54	$116.55	$116.50
Purchase #5	$247.51	3.678%	$256.6134	$256.61	$256.60	$256.60
Purchase #6	$78.61	12.736%	$88.6218	$88.62	$88.60	$88.60
Purchase #7	$51.50	5.783%	$54.4782	$54.48	$54.50	$54.50
7 purchase totals =	$772.63		$821.2188	$821.22	$821.20	$821.20