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	$249.92	8.545%	$271.2757	$271.28	$271.30	$271.30
Purchase #2	$216.77	12.371%	$243.5866	$243.59	$243.60	$243.60
Purchase #3	$186.55	12.641%	$210.1318	$210.13	$210.15	$210.10
Purchase #4	$70.39	3.303%	$72.715	$72.72	$72.70	$72.70
Purchase #5	$37.60	11.742%	$42.015	$42.02	$42.00	$42.00
Purchase #6	$24.75	9.740%	$27.1607	$27.16	$27.15	$27.20
Purchase #7	$13.75	11.741%	$15.3644	$15.36	$15.35	$15.40
7 purchase totals =	$799.73		$882.2492	$882.26	$882.25	$882.30