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	$47.74	12.733%	$53.8187	$53.82	$53.80	$53.80
Purchase #2	$55.67	7.366%	$59.7707	$59.77	$59.75	$59.80
Purchase #3	$170.93	5.233%	$179.8748	$179.87	$179.85	$179.90
Purchase #4	$84.43	7.132%	$90.4515	$90.45	$90.45	$90.50
Purchase #5	$93.90	4.868%	$98.4711	$98.47	$98.45	$98.50
Purchase #6	$144.64	5.102%	$152.0195	$152.02	$152.00	$152.00
Purchase #7	$45.32	13.760%	$51.556	$51.56	$51.55	$51.60
7 purchase totals =	$642.63		$685.9623	$685.96	$685.85	$686.10