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	$62.61	7.508%	$67.3108	$67.31	$67.30	$67.30
Purchase #2	$101.84	6.698%	$108.6612	$108.66	$108.65	$108.70
Purchase #3	$83.37	6.421%	$88.7232	$88.72	$88.70	$88.70
Purchase #4	$174.59	13.665%	$198.4477	$198.45	$198.45	$198.40
Purchase #5	$229.91	8.664%	$249.8294	$249.83	$249.85	$249.80
Purchase #6	$202.41	3.558%	$209.6117	$209.61	$209.60	$209.60
Purchase #7	$32.54	3.539%	$33.6916	$33.69	$33.70	$33.70
7 purchase totals =	$887.27		$956.2756	$956.27	$956.25	$956.20