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	$42.60	4.195%	$44.3871	$44.39	$44.40	$44.40
Purchase #2	$75.58	3.579%	$78.285	$78.29	$78.30	$78.30
Purchase #3	$135.43	7.258%	$145.2595	$145.26	$145.25	$145.30
Purchase #4	$83.65	7.871%	$90.2341	$90.23	$90.25	$90.20
Purchase #5	$19.72	3.498%	$20.4098	$20.41	$20.40	$20.40
Purchase #6	$102.51	7.737%	$110.4412	$110.44	$110.45	$110.40
Purchase #7	$92.60	10.392%	$102.223	$102.22	$102.20	$102.20
7 purchase totals =	$552.09		$591.2397	$591.24	$591.25	$591.20