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	$37.78	10.657%	$41.8062	$41.81	$41.80	$41.80
Purchase #2	$217.88	10.447%	$240.6419	$240.64	$240.65	$240.60
Purchase #3	$154.96	8.874%	$168.7112	$168.71	$168.70	$168.70
Purchase #4	$222.94	10.536%	$246.429	$246.43	$246.45	$246.40
Purchase #5	$47.36	12.144%	$53.1114	$53.11	$53.10	$53.10
Purchase #6	$110.70	11.502%	$123.4327	$123.43	$123.45	$123.40
Purchase #7	$95.82	4.674%	$100.2986	$100.30	$100.30	$100.30
7 purchase totals =	$887.44		$974.4310	$974.43	$974.45	$974.30