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	7.650%	$17.9022	$17.90	$17.90	$17.90
Purchase #2	$213.80	8.268%	$231.477	$231.48	$231.50	$231.50
Purchase #3	$47.66	9.424%	$52.1515	$52.15	$52.15	$52.20
Purchase #4	$50.93	3.869%	$52.9005	$52.90	$52.90	$52.90
Purchase #5	$142.69	9.653%	$156.4639	$156.46	$156.45	$156.50
Purchase #6	$37.94	6.158%	$40.2763	$40.28	$40.30	$40.30
Purchase #7	$53.72	6.267%	$57.0866	$57.09	$57.10	$57.10
7 purchase totals =	$563.37		$608.2580	$608.26	$608.30	$608.40