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	$221.56	8.658%	$240.7427	$240.74	$240.75	$240.70
Purchase #2	$168.94	11.333%	$188.086	$188.09	$188.10	$188.10
Purchase #3	$41.33	3.744%	$42.8774	$42.88	$42.90	$42.90
Purchase #4	$29.55	12.501%	$33.244	$33.24	$33.25	$33.20
Purchase #5	$133.44	9.235%	$145.7632	$145.76	$145.75	$145.80
Purchase #6	$146.82	10.299%	$161.941	$161.94	$161.95	$161.90
Purchase #7	$14.51	9.537%	$15.8938	$15.89	$15.90	$15.90
7 purchase totals =	$756.15		$828.5481	$828.54	$828.60	$828.50