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	$31.62	10.170%	$34.8358	$34.84	$34.85	$34.80
Purchase #2	$197.56	9.749%	$216.8201	$216.82	$216.80	$216.80
Purchase #3	$12.60	3.597%	$13.0532	$13.05	$13.05	$13.10
Purchase #4	$141.34	8.135%	$152.838	$152.84	$152.85	$152.80
Purchase #5	$5.46	7.304%	$5.8588	$5.86	$5.85	$5.90
Purchase #6	$37.81	12.420%	$42.506	$42.51	$42.50	$42.50
Purchase #7	$39.74	7.758%	$42.823	$42.82	$42.80	$42.80
7 purchase totals =	$466.13		$508.7349	$508.74	$508.70	$508.70