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	$243.39	8.659%	$264.4651	$264.47	$264.45	$264.50
Purchase #2	$90.76	13.822%	$103.3048	$103.30	$103.30	$103.30
Purchase #3	$124.79	9.248%	$136.3306	$136.33	$136.35	$136.30
Purchase #4	$229.44	5.240%	$241.4627	$241.46	$241.45	$241.50
Purchase #5	$16.67	10.282%	$18.384	$18.38	$18.40	$18.40
Purchase #6	$73.46	13.296%	$83.2272	$83.23	$83.25	$83.20
Purchase #7	$57.65	12.442%	$64.8228	$64.82	$64.80	$64.80
7 purchase totals =	$836.16		$911.9972	$911.99	$912.00	$912.00