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	$11.66	4.186%	$12.1481	$12.15	$12.15	$12.10
Purchase #2	$73.81	12.219%	$82.8288	$82.83	$82.85	$82.80
Purchase #3	$151.57	11.369%	$168.802	$168.80	$168.80	$168.80
Purchase #4	$59.49	10.788%	$65.9078	$65.91	$65.90	$65.90
Purchase #5	$187.44	6.457%	$199.543	$199.54	$199.55	$199.50
Purchase #6	$6.86	9.670%	$7.5234	$7.52	$7.50	$7.50
Purchase #7	$115.42	11.819%	$129.0615	$129.06	$129.05	$129.10
7 purchase totals =	$606.25		$665.8146	$665.81	$665.80	$665.70