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	$25.56	10.316%	$28.1968	$28.20	$28.20	$28.20
Purchase #2	$63.79	13.203%	$72.2122	$72.21	$72.20	$72.20
Purchase #3	$67.38	8.146%	$72.8688	$72.87	$72.85	$72.90
Purchase #4	$189.38	5.336%	$199.4853	$199.49	$199.50	$199.50
Purchase #5	$40.44	8.532%	$43.8903	$43.89	$43.90	$43.90
Purchase #6	$40.99	5.384%	$43.1969	$43.20	$43.20	$43.20
Purchase #7	$192.55	9.491%	$210.8249	$210.82	$210.80	$210.80
7 purchase totals =	$620.09		$670.6752	$670.68	$670.65	$670.70