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	$16.63	5.258%	$17.5044	$17.50	$17.50	$17.50
Purchase #2	$69.90	12.479%	$78.6228	$78.62	$78.60	$78.60
Purchase #3	$206.67	7.832%	$222.8564	$222.86	$222.85	$222.90
Purchase #4	$16.67	12.606%	$18.7714	$18.77	$18.75	$18.80
Purchase #5	$86.66	13.192%	$98.0922	$98.09	$98.10	$98.10
Purchase #6	$140.82	5.148%	$148.0694	$148.07	$148.05	$148.10
Purchase #7	$46.74	10.218%	$51.5159	$51.52	$51.50	$51.50
7 purchase totals =	$584.09		$635.4325	$635.43	$635.35	$635.50