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	$241.49	5.550%	$254.8927	$254.89	$254.90	$254.90
Purchase #2	$185.65	13.766%	$211.2066	$211.21	$211.20	$211.20
Purchase #3	$19.31	5.752%	$20.4207	$20.42	$20.40	$20.40
Purchase #4	$74.86	7.178%	$80.2335	$80.23	$80.25	$80.20
Purchase #5	$81.58	12.520%	$91.7938	$91.79	$91.80	$91.80
Purchase #6	$139.39	3.770%	$144.645	$144.65	$144.65	$144.60
Purchase #7	$243.38	13.265%	$275.6644	$275.66	$275.65	$275.70
7 purchase totals =	$985.66		$1,078.8567	$1,078.85	$1,078.85	$1,078.80