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	$51.89	6.277%	$55.1471	$55.15	$55.15	$55.10
Purchase #2	$70.59	12.283%	$79.2606	$79.26	$79.25	$79.30
Purchase #3	$189.58	4.720%	$198.5282	$198.53	$198.55	$198.50
Purchase #4	$80.63	5.753%	$85.2686	$85.27	$85.25	$85.30
Purchase #5	$167.38	13.638%	$190.2073	$190.21	$190.20	$190.20
Purchase #6	$32.39	7.502%	$34.8199	$34.82	$34.80	$34.80
Purchase #7	$34.34	13.148%	$38.855	$38.86	$38.85	$38.90
7 purchase totals =	$626.80		$682.0867	$682.10	$682.05	$682.10