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	$18.98	8.580%	$20.6085	$20.61	$20.60	$20.60
Purchase #2	$89.60	13.651%	$101.8313	$101.83	$101.85	$101.80
Purchase #3	$53.96	3.421%	$55.806	$55.81	$55.80	$55.80
Purchase #4	$73.86	5.627%	$78.0161	$78.02	$78.00	$78.00
Purchase #5	$148.33	9.594%	$162.5608	$162.56	$162.55	$162.60
Purchase #6	$72.91	5.793%	$77.1337	$77.13	$77.15	$77.10
Purchase #7	$204.46	9.623%	$224.1352	$224.14	$224.15	$224.10
7 purchase totals =	$662.10		$720.0916	$720.10	$720.10	$720.00