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	$178.69	3.722%	$185.3408	$185.34	$185.35	$185.30
Purchase #2	$144.72	8.545%	$157.0863	$157.09	$157.10	$157.10
Purchase #3	$54.67	9.445%	$59.8336	$59.83	$59.85	$59.80
Purchase #4	$220.71	9.131%	$240.863	$240.86	$240.85	$240.90
Purchase #5	$183.82	12.784%	$207.3195	$207.32	$207.30	$207.30
Purchase #6	$128.97	6.323%	$137.1248	$137.12	$137.10	$137.10
Purchase #7	$208.91	12.419%	$234.8545	$234.85	$234.85	$234.90
7 purchase totals =	$1,120.49		$1,222.4225	$1,222.41	$1,222.40	$1,222.40