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	$94.59	4.132%	$98.4985	$98.50	$98.50	$98.50
Purchase #2	$135.75	5.563%	$143.3018	$143.30	$143.30	$143.30
Purchase #3	$87.65	13.386%	$99.3828	$99.38	$99.40	$99.40
Purchase #4	$59.73	9.689%	$65.5172	$65.52	$65.50	$65.50
Purchase #5	$83.27	8.846%	$90.6361	$90.64	$90.65	$90.60
Purchase #6	$208.69	9.194%	$227.877	$227.88	$227.90	$227.90
Purchase #7	$205.38	13.481%	$233.0673	$233.07	$233.05	$233.10
7 purchase totals =	$875.06		$958.2807	$958.29	$958.30	$958.30