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	$57.63	12.549%	$64.862	$64.86	$64.85	$64.90
Purchase #2	$128.64	10.295%	$141.8835	$141.88	$141.90	$141.90
Purchase #3	$206.51	8.270%	$223.5884	$223.59	$223.60	$223.60
Purchase #4	$162.71	5.692%	$171.9715	$171.97	$171.95	$172.00
Purchase #5	$91.49	3.288%	$94.4982	$94.50	$94.50	$94.50
Purchase #6	$88.27	8.203%	$95.5108	$95.51	$95.50	$95.50
Purchase #7	$217.71	9.730%	$238.8932	$238.89	$238.90	$238.90
7 purchase totals =	$952.96		$1,031.2076	$1,031.20	$1,031.20	$1,031.30