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	$166.86	5.319%	$175.7353	$175.74	$175.75	$175.70
Purchase #2	$52.69	7.766%	$56.7819	$56.78	$56.80	$56.80
Purchase #3	$178.72	10.475%	$197.4409	$197.44	$197.45	$197.40
Purchase #4	$60.48	10.600%	$66.8909	$66.89	$66.90	$66.90
Purchase #5	$152.95	8.865%	$166.509	$166.51	$166.50	$166.50
Purchase #6	$184.71	3.690%	$191.5258	$191.53	$191.55	$191.50
Purchase #7	$208.69	12.344%	$234.4507	$234.45	$234.45	$234.50
7 purchase totals =	$1,005.10		$1,089.3345	$1,089.34	$1,089.40	$1,089.30