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	$92.30	8.211%	$99.8788	$99.88	$99.90	$99.90
Purchase #2	$182.38	4.873%	$191.2674	$191.27	$191.25	$191.30
Purchase #3	$156.46	5.829%	$165.5801	$165.58	$165.60	$165.60
Purchase #4	$119.73	7.487%	$128.6942	$128.69	$128.70	$128.70
Purchase #5	$169.96	12.152%	$190.6135	$190.61	$190.60	$190.60
Purchase #6	$112.44	6.514%	$119.7643	$119.76	$119.75	$119.80
Purchase #7	$34.81	5.384%	$36.6842	$36.68	$36.70	$36.70
7 purchase totals =	$868.08		$932.4825	$932.47	$932.50	$932.60