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	$232.67	3.295%	$240.3365	$240.34	$240.35	$240.30
Purchase #2	$157.42	13.565%	$178.774	$178.77	$178.75	$178.80
Purchase #3	$119.97	3.832%	$124.5673	$124.57	$124.55	$124.60
Purchase #4	$21.85	11.408%	$24.3426	$24.34	$24.35	$24.30
Purchase #5	$228.89	11.175%	$254.4685	$254.47	$254.45	$254.50
Purchase #6	$60.48	10.578%	$66.8776	$66.88	$66.90	$66.90
Purchase #7	$103.47	10.694%	$114.5351	$114.54	$114.55	$114.50
7 purchase totals =	$924.75		$1,003.9016	$1,003.91	$1,003.90	$1,003.90