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	$14.41	7.439%	$15.482	$15.48	$15.50	$15.50
Purchase #2	$163.47	13.651%	$185.7853	$185.79	$185.80	$185.80
Purchase #3	$33.41	10.803%	$37.0193	$37.02	$37.00	$37.00
Purchase #4	$79.61	8.429%	$86.3203	$86.32	$86.30	$86.30
Purchase #5	$81.62	10.472%	$90.1672	$90.17	$90.15	$90.20
Purchase #6	$245.25	10.347%	$270.626	$270.63	$270.65	$270.60
Purchase #7	$13.94	8.467%	$15.1203	$15.12	$15.10	$15.10
7 purchase totals =	$631.71		$700.5204	$700.53	$700.50	$700.50