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	$42.76	5.587%	$45.149	$45.15	$45.15	$45.10
Purchase #2	$42.96	9.798%	$47.1692	$47.17	$47.15	$47.20
Purchase #3	$28.60	11.215%	$31.8075	$31.81	$31.80	$31.80
Purchase #4	$23.62	13.640%	$26.8418	$26.84	$26.85	$26.80
Purchase #5	$157.47	4.489%	$164.5388	$164.54	$164.55	$164.50
Purchase #6	$100.58	7.130%	$107.7514	$107.75	$107.75	$107.80
Purchase #7	$93.89	12.461%	$105.5896	$105.59	$105.60	$105.60
7 purchase totals =	$489.88		$528.8473	$528.85	$528.85	$528.80