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	$114.79	5.764%	$121.4065	$121.41	$121.40	$121.40
Purchase #2	$235.40	5.374%	$248.0504	$248.05	$248.05	$248.10
Purchase #3	$7.57	3.735%	$7.8527	$7.85	$7.85	$7.90
Purchase #4	$153.30	13.771%	$174.4109	$174.41	$174.40	$174.40
Purchase #5	$39.53	9.712%	$43.3692	$43.37	$43.35	$43.40
Purchase #6	$222.58	3.805%	$231.0492	$231.05	$231.05	$231.00
Purchase #7	$136.32	11.758%	$152.3485	$152.35	$152.35	$152.30
7 purchase totals =	$909.49		$978.4874	$978.49	$978.45	$978.50