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	$22.41	3.256%	$23.1397	$23.14	$23.15	$23.10
Purchase #2	$76.61	7.752%	$82.5488	$82.55	$82.55	$82.50
Purchase #3	$142.90	8.584%	$155.1665	$155.17	$155.15	$155.20
Purchase #4	$99.44	12.510%	$111.8799	$111.88	$111.90	$111.90
Purchase #5	$22.44	10.346%	$24.7616	$24.76	$24.75	$24.80
Purchase #6	$38.61	10.769%	$42.7679	$42.77	$42.75	$42.80
Purchase #7	$211.79	3.396%	$218.9824	$218.98	$219.00	$219.00
7 purchase totals =	$614.20		$659.2468	$659.25	$659.25	$659.30