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	$38.49	10.673%	$42.598	$42.60	$42.60	$42.60
Purchase #2	$43.61	8.677%	$47.394	$47.39	$47.40	$47.40
Purchase #3	$179.76	3.157%	$185.435	$185.44	$185.45	$185.40
Purchase #4	$149.62	12.258%	$167.9604	$167.96	$167.95	$168.00
Purchase #5	$166.28	6.351%	$176.8404	$176.84	$176.85	$176.80
Purchase #6	$163.94	13.422%	$185.944	$185.94	$185.95	$185.90
Purchase #7	$82.89	8.865%	$90.2382	$90.24	$90.25	$90.20
7 purchase totals =	$824.59		$896.4100	$896.41	$896.45	$896.30