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	$55.36	7.844%	$59.7024	$59.70	$59.70	$59.70
Purchase #2	$83.92	7.429%	$90.1544	$90.15	$90.15	$90.20
Purchase #3	$185.90	7.109%	$199.1156	$199.12	$199.10	$199.10
Purchase #4	$61.40	5.762%	$64.9379	$64.94	$64.95	$64.90
Purchase #5	$117.63	12.853%	$132.749	$132.75	$132.75	$132.70
Purchase #6	$215.25	7.440%	$231.2646	$231.26	$231.25	$231.30
Purchase #7	$58.69	11.448%	$65.4088	$65.41	$65.40	$65.40
7 purchase totals =	$778.15		$843.3327	$843.33	$843.30	$843.30