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	$98.25	6.538%	$104.6736	$104.67	$104.65	$104.70
Purchase #2	$78.88	5.116%	$82.9155	$82.92	$82.90	$82.90
Purchase #3	$88.91	11.443%	$99.084	$99.08	$99.10	$99.10
Purchase #4	$80.76	11.126%	$89.7454	$89.75	$89.75	$89.70
Purchase #5	$206.71	13.412%	$234.4339	$234.43	$234.45	$234.40
Purchase #6	$17.27	3.388%	$17.8551	$17.86	$17.85	$17.90
Purchase #7	$38.82	5.256%	$40.8604	$40.86	$40.85	$40.90
7 purchase totals =	$609.60		$669.5679	$669.57	$669.55	$669.60