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	$18.98	8.784%	$20.6472	$20.65	$20.65	$20.60
Purchase #2	$234.51	11.488%	$261.4505	$261.45	$261.45	$261.50
Purchase #3	$100.76	3.694%	$104.4821	$104.48	$104.50	$104.50
Purchase #4	$104.95	3.787%	$108.9245	$108.92	$108.90	$108.90
Purchase #5	$187.82	12.540%	$211.3726	$211.37	$211.35	$211.40
Purchase #6	$204.78	11.865%	$229.0771	$229.08	$229.10	$229.10
Purchase #7	$245.91	7.743%	$264.9508	$264.95	$264.95	$265.00
7 purchase totals =	$1,097.71		$1,200.9048	$1,200.90	$1,200.90	$1,201.00