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	$99.96	13.341%	$113.2957	$113.30	$113.30	$113.30
Purchase #2	$163.41	11.764%	$182.6336	$182.63	$182.65	$182.60
Purchase #3	$62.71	7.667%	$67.518	$67.52	$67.50	$67.50
Purchase #4	$43.40	11.626%	$48.4457	$48.45	$48.45	$48.40
Purchase #5	$190.78	3.220%	$196.9231	$196.92	$196.90	$196.90
Purchase #6	$116.65	12.764%	$131.5392	$131.54	$131.55	$131.50
Purchase #7	$73.37	9.733%	$80.5111	$80.51	$80.50	$80.50
7 purchase totals =	$750.28		$820.8664	$820.87	$820.85	$820.70