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	$154.75	4.151%	$161.1737	$161.17	$161.15	$161.20
Purchase #2	$175.48	10.289%	$193.5351	$193.54	$193.55	$193.50
Purchase #3	$169.54	9.709%	$186.0006	$186.00	$186.00	$186.00
Purchase #4	$99.56	12.354%	$111.8596	$111.86	$111.85	$111.90
Purchase #5	$12.70	3.704%	$13.1704	$13.17	$13.15	$13.20
Purchase #6	$78.39	13.458%	$88.9397	$88.94	$88.95	$88.90
Purchase #7	$88.31	3.527%	$91.4247	$91.42	$91.40	$91.40
7 purchase totals =	$778.73		$846.1038	$846.10	$846.05	$846.10