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	$84.77	6.393%	$90.1893	$90.19	$90.20	$90.20
Purchase #2	$76.39	8.733%	$83.0611	$83.06	$83.05	$83.10
Purchase #3	$82.76	8.291%	$89.6216	$89.62	$89.60	$89.60
Purchase #4	$6.86	8.545%	$7.4462	$7.45	$7.45	$7.40
Purchase #5	$81.79	4.181%	$85.2096	$85.21	$85.20	$85.20
Purchase #6	$115.47	10.744%	$127.8761	$127.88	$127.90	$127.90
Purchase #7	$165.34	3.599%	$171.2906	$171.29	$171.30	$171.30
7 purchase totals =	$613.38		$654.6945	$654.70	$654.70	$654.70