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	$41.34	3.574%	$42.8175	$42.82	$42.80	$42.80
Purchase #2	$100.87	5.464%	$106.3815	$106.38	$106.40	$106.40
Purchase #3	$56.62	13.146%	$64.0633	$64.06	$64.05	$64.10
Purchase #4	$63.29	13.474%	$71.8177	$71.82	$71.80	$71.80
Purchase #5	$131.25	4.720%	$137.445	$137.45	$137.45	$137.40
Purchase #6	$235.41	10.404%	$259.9021	$259.90	$259.90	$259.90
Purchase #7	$21.39	7.464%	$22.9865	$22.99	$23.00	$23.00
7 purchase totals =	$650.17		$705.4136	$705.42	$705.40	$705.40