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	$35.83	12.862%	$40.4385	$40.44	$40.45	$40.40
Purchase #2	$116.62	13.460%	$132.3171	$132.32	$132.30	$132.30
Purchase #3	$202.83	6.777%	$216.5758	$216.58	$216.60	$216.60
Purchase #4	$178.38	5.564%	$188.3051	$188.31	$188.30	$188.30
Purchase #5	$127.51	4.618%	$133.3984	$133.40	$133.40	$133.40
Purchase #6	$38.63	7.381%	$41.4813	$41.48	$41.50	$41.50
Purchase #7	$64.57	10.807%	$71.5481	$71.55	$71.55	$71.50
7 purchase totals =	$764.37		$824.0643	$824.08	$824.10	$824.00