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	$106.48	11.164%	$118.3674	$118.37	$118.35	$118.40
Purchase #2	$174.48	8.541%	$189.3823	$189.38	$189.40	$189.40
Purchase #3	$89.80	7.577%	$96.6041	$96.60	$96.60	$96.60
Purchase #4	$133.71	13.150%	$151.2929	$151.29	$151.30	$151.30
Purchase #5	$174.54	8.390%	$189.1839	$189.18	$189.20	$189.20
Purchase #6	$80.93	12.421%	$90.9823	$90.98	$91.00	$91.00
Purchase #7	$118.86	12.167%	$133.3217	$133.32	$133.30	$133.30
7 purchase totals =	$878.80		$969.1346	$969.12	$969.15	$969.20