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	$91.35	9.366%	$99.9058	$99.91	$99.90	$99.90
Purchase #2	$76.68	7.462%	$82.4019	$82.40	$82.40	$82.40
Purchase #3	$97.57	9.289%	$106.6333	$106.63	$106.65	$106.60
Purchase #4	$213.55	9.863%	$234.6124	$234.61	$234.60	$234.60
Purchase #5	$66.66	6.695%	$71.1229	$71.12	$71.10	$71.10
Purchase #6	$226.40	13.335%	$256.5904	$256.59	$256.60	$256.60
Purchase #7	$143.90	8.837%	$156.6164	$156.62	$156.60	$156.60
7 purchase totals =	$916.11		$1,007.8831	$1,007.88	$1,007.85	$1,007.80