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	$52.93	12.701%	$59.6526	$59.65	$59.65	$59.70
Purchase #2	$210.56	8.288%	$228.0112	$228.01	$228.00	$228.00
Purchase #3	$37.32	9.602%	$40.9035	$40.90	$40.90	$40.90
Purchase #4	$159.87	12.283%	$179.5068	$179.51	$179.50	$179.50
Purchase #5	$15.36	11.159%	$17.074	$17.07	$17.05	$17.10
Purchase #6	$46.49	9.534%	$50.9224	$50.92	$50.90	$50.90
Purchase #7	$77.30	4.688%	$80.9238	$80.92	$80.90	$80.90
7 purchase totals =	$599.83		$656.9943	$656.98	$656.90	$657.00