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	$63.61	3.534%	$65.858	$65.86	$65.85	$65.90
Purchase #2	$19.93	7.777%	$21.48	$21.48	$21.50	$21.50
Purchase #3	$217.64	12.791%	$245.4783	$245.48	$245.50	$245.50
Purchase #4	$245.68	6.590%	$261.8703	$261.87	$261.85	$261.90
Purchase #5	$57.92	6.310%	$61.5748	$61.57	$61.55	$61.60
Purchase #6	$18.93	11.804%	$21.1645	$21.16	$21.15	$21.20
Purchase #7	$129.81	9.483%	$142.1199	$142.12	$142.10	$142.10
7 purchase totals =	$753.52		$819.5458	$819.54	$819.50	$819.70