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	$17.47	10.671%	$19.3342	$19.33	$19.35	$19.30
Purchase #2	$150.99	7.554%	$162.3958	$162.40	$162.40	$162.40
Purchase #3	$71.81	9.112%	$78.3533	$78.35	$78.35	$78.40
Purchase #4	$19.54	7.441%	$20.994	$20.99	$21.00	$21.00
Purchase #5	$191.64	5.639%	$202.4466	$202.45	$202.45	$202.40
Purchase #6	$63.64	11.121%	$70.7174	$70.72	$70.70	$70.70
Purchase #7	$82.89	7.384%	$89.0106	$89.01	$89.00	$89.00
7 purchase totals =	$597.98		$643.2519	$643.25	$643.25	$643.20