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	$47.42	3.166%	$48.9213	$48.92	$48.90	$48.90
Purchase #2	$102.27	9.310%	$111.7913	$111.79	$111.80	$111.80
Purchase #3	$79.60	13.371%	$90.2433	$90.24	$90.25	$90.20
Purchase #4	$215.54	12.234%	$241.9092	$241.91	$241.90	$241.90
Purchase #5	$151.51	5.213%	$159.4082	$159.41	$159.40	$159.40
Purchase #6	$62.47	13.200%	$70.716	$70.72	$70.70	$70.70
Purchase #7	$195.74	6.387%	$208.2419	$208.24	$208.25	$208.20
7 purchase totals =	$854.55		$931.2312	$931.23	$931.20	$931.10