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	$240.72	3.766%	$249.7855	$249.79	$249.80	$249.80
Purchase #2	$226.96	10.469%	$250.7204	$250.72	$250.70	$250.70
Purchase #3	$99.32	10.676%	$109.9234	$109.92	$109.90	$109.90
Purchase #4	$152.69	12.293%	$171.4602	$171.46	$171.45	$171.50
Purchase #5	$22.31	8.704%	$24.2519	$24.25	$24.25	$24.30
Purchase #6	$38.62	9.373%	$42.2399	$42.24	$42.25	$42.20
Purchase #7	$16.92	11.190%	$18.8133	$18.81	$18.80	$18.80
7 purchase totals =	$797.54		$867.1946	$867.19	$867.15	$867.20