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	$21.58	12.330%	$24.2408	$24.24	$24.25	$24.20
Purchase #2	$161.89	12.669%	$182.3998	$182.40	$182.40	$182.40
Purchase #3	$100.81	3.414%	$104.2517	$104.25	$104.25	$104.30
Purchase #4	$84.69	11.556%	$94.4768	$94.48	$94.50	$94.50
Purchase #5	$154.82	11.675%	$172.8952	$172.90	$172.90	$172.90
Purchase #6	$209.47	6.508%	$223.1023	$223.10	$223.10	$223.10
Purchase #7	$60.60	12.383%	$68.1041	$68.10	$68.10	$68.10
7 purchase totals =	$793.86		$869.4707	$869.47	$869.50	$869.50