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	$42.89	7.318%	$46.0287	$46.03	$46.05	$46.00
Purchase #2	$236.31	3.256%	$244.0043	$244.00	$244.00	$244.00
Purchase #3	$199.71	10.265%	$220.2102	$220.21	$220.20	$220.20
Purchase #4	$193.85	13.153%	$219.3471	$219.35	$219.35	$219.30
Purchase #5	$75.67	8.538%	$82.1307	$82.13	$82.15	$82.10
Purchase #6	$72.90	7.614%	$78.4506	$78.45	$78.45	$78.50
Purchase #7	$85.66	5.471%	$90.3465	$90.35	$90.35	$90.30
7 purchase totals =	$906.99		$980.5181	$980.52	$980.55	$980.40