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	$76.56	7.778%	$82.5148	$82.51	$82.50	$82.50
Purchase #2	$187.62	6.761%	$200.305	$200.31	$200.30	$200.30
Purchase #3	$225.53	5.802%	$238.6153	$238.62	$238.60	$238.60
Purchase #4	$206.29	8.662%	$224.1588	$224.16	$224.15	$224.20
Purchase #5	$128.37	4.529%	$134.1839	$134.18	$134.20	$134.20
Purchase #6	$89.94	12.578%	$101.2527	$101.25	$101.25	$101.30
Purchase #7	$123.50	4.109%	$128.5746	$128.57	$128.55	$128.60
7 purchase totals =	$1,037.81		$1,109.6051	$1,109.60	$1,109.55	$1,109.70