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	$38.25	12.307%	$42.9574	$42.96	$42.95	$43.00
Purchase #2	$37.45	8.196%	$40.5194	$40.52	$40.50	$40.50
Purchase #3	$248.48	9.677%	$272.5254	$272.53	$272.55	$272.50
Purchase #4	$167.74	10.768%	$185.8022	$185.80	$185.80	$185.80
Purchase #5	$179.71	8.791%	$195.5083	$195.51	$195.50	$195.50
Purchase #6	$14.59	6.711%	$15.5691	$15.57	$15.55	$15.60
Purchase #7	$110.41	11.434%	$123.0343	$123.03	$123.05	$123.00
7 purchase totals =	$796.63		$875.9161	$875.92	$875.90	$875.90