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	$92.64	7.599%	$99.6797	$99.68	$99.70	$99.70
Purchase #2	$29.41	6.560%	$31.3393	$31.34	$31.35	$31.30
Purchase #3	$169.82	10.472%	$187.6036	$187.60	$187.60	$187.60
Purchase #4	$27.98	7.782%	$30.1574	$30.16	$30.15	$30.20
Purchase #5	$86.42	4.511%	$90.3184	$90.32	$90.30	$90.30
Purchase #6	$246.92	13.728%	$280.8172	$280.82	$280.80	$280.80
Purchase #7	$188.29	10.480%	$208.0228	$208.02	$208.00	$208.00
7 purchase totals =	$841.48		$927.9384	$927.94	$927.90	$927.90