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	$83.54	8.802%	$90.8932	$90.89	$90.90	$90.90
Purchase #2	$95.86	9.795%	$105.2495	$105.25	$105.25	$105.20
Purchase #3	$198.27	10.176%	$218.446	$218.45	$218.45	$218.40
Purchase #4	$135.74	9.337%	$148.414	$148.41	$148.40	$148.40
Purchase #5	$28.93	5.621%	$30.5562	$30.56	$30.55	$30.60
Purchase #6	$243.27	4.629%	$254.531	$254.53	$254.55	$254.50
Purchase #7	$103.88	7.190%	$111.349	$111.35	$111.35	$111.30
7 purchase totals =	$889.49		$959.4389	$959.44	$959.45	$959.30