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	$91.59	8.815%	$99.6637	$99.66	$99.65	$99.70
Purchase #2	$204.73	8.188%	$221.4933	$221.49	$221.50	$221.50
Purchase #3	$194.50	10.620%	$215.1559	$215.16	$215.15	$215.20
Purchase #4	$91.94	11.708%	$102.7043	$102.70	$102.70	$102.70
Purchase #5	$59.34	13.811%	$67.5354	$67.54	$67.55	$67.50
Purchase #6	$148.25	11.572%	$165.4055	$165.41	$165.40	$165.40
Purchase #7	$80.55	7.580%	$86.6557	$86.66	$86.65	$86.70
7 purchase totals =	$870.90		$958.6138	$958.62	$958.60	$958.70