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	$82.69	9.617%	$90.6423	$90.64	$90.65	$90.60
Purchase #2	$117.62	9.217%	$128.461	$128.46	$128.45	$128.50
Purchase #3	$138.93	8.615%	$150.8988	$150.90	$150.90	$150.90
Purchase #4	$218.52	11.300%	$243.2128	$243.21	$243.20	$243.20
Purchase #5	$83.90	8.559%	$91.081	$91.08	$91.10	$91.10
Purchase #6	$99.89	3.545%	$103.4311	$103.43	$103.45	$103.40
Purchase #7	$77.38	12.639%	$87.1601	$87.16	$87.15	$87.20
7 purchase totals =	$818.93		$894.8871	$894.88	$894.90	$894.90