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	$16.72	9.870%	$18.3703	$18.37	$18.35	$18.40
Purchase #2	$146.64	6.629%	$156.3608	$156.36	$156.35	$156.40
Purchase #3	$236.25	7.238%	$253.3498	$253.35	$253.35	$253.30
Purchase #4	$211.33	13.162%	$239.1453	$239.15	$239.15	$239.10
Purchase #5	$53.25	11.280%	$59.2566	$59.26	$59.25	$59.30
Purchase #6	$136.53	5.459%	$143.9832	$143.98	$144.00	$144.00
Purchase #7	$233.44	5.443%	$246.1461	$246.15	$246.15	$246.10
7 purchase totals =	$1,034.16		$1,116.6121	$1,116.62	$1,116.60	$1,116.60