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	$37.60	7.766%	$40.52	$40.52	$40.50	$40.50
Purchase #2	$225.79	6.530%	$240.5341	$240.53	$240.55	$240.50
Purchase #3	$89.67	13.858%	$102.0965	$102.10	$102.10	$102.10
Purchase #4	$109.94	12.397%	$123.5693	$123.57	$123.55	$123.60
Purchase #5	$130.64	3.270%	$134.9119	$134.91	$134.90	$134.90
Purchase #6	$30.43	11.497%	$33.9285	$33.93	$33.95	$33.90
Purchase #7	$171.63	11.297%	$191.019	$191.02	$191.00	$191.00
7 purchase totals =	$795.70		$866.5793	$866.58	$866.55	$866.50