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	$13.87	11.263%	$15.4322	$15.43	$15.45	$15.40
Purchase #2	$55.69	10.269%	$61.4088	$61.41	$61.40	$61.40
Purchase #3	$103.57	9.471%	$113.3791	$113.38	$113.40	$113.40
Purchase #4	$28.53	13.709%	$32.4412	$32.44	$32.45	$32.40
Purchase #5	$86.89	7.656%	$93.5423	$93.54	$93.55	$93.50
Purchase #6	$46.74	8.393%	$50.6629	$50.66	$50.65	$50.70
Purchase #7	$179.90	6.487%	$191.5701	$191.57	$191.55	$191.60
7 purchase totals =	$515.19		$558.4366	$558.43	$558.45	$558.40