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	$82.59	7.803%	$89.0345	$89.03	$89.05	$89.00
Purchase #2	$77.96	10.204%	$85.915	$85.92	$85.90	$85.90
Purchase #3	$63.30	13.618%	$71.9202	$71.92	$71.90	$71.90
Purchase #4	$116.56	7.551%	$125.3614	$125.36	$125.35	$125.40
Purchase #5	$57.38	9.624%	$62.9023	$62.90	$62.90	$62.90
Purchase #6	$223.54	8.469%	$242.4716	$242.47	$242.45	$242.50
Purchase #7	$189.45	3.409%	$195.9084	$195.91	$195.90	$195.90
7 purchase totals =	$810.78		$873.5134	$873.51	$873.45	$873.50