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	$40.52	4.367%	$42.2895	$42.29	$42.30	$42.30
Purchase #2	$76.52	8.102%	$82.7197	$82.72	$82.70	$82.70
Purchase #3	$87.91	7.527%	$94.527	$94.53	$94.55	$94.50
Purchase #4	$168.84	10.650%	$186.8215	$186.82	$186.80	$186.80
Purchase #5	$62.47	3.166%	$64.4478	$64.45	$64.45	$64.40
Purchase #6	$53.85	10.507%	$59.508	$59.51	$59.50	$59.50
Purchase #7	$100.65	12.513%	$113.2443	$113.24	$113.25	$113.20
7 purchase totals =	$590.76		$643.5578	$643.56	$643.55	$643.40