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	$46.34	8.508%	$50.2826	$50.28	$50.30	$50.30
Purchase #2	$159.95	7.829%	$172.4725	$172.47	$172.45	$172.50
Purchase #3	$215.66	3.801%	$223.8572	$223.86	$223.85	$223.90
Purchase #4	$238.70	10.121%	$262.8588	$262.86	$262.85	$262.90
Purchase #5	$230.38	13.688%	$261.9144	$261.91	$261.90	$261.90
Purchase #6	$233.81	8.745%	$254.2567	$254.26	$254.25	$254.30
Purchase #7	$152.71	6.542%	$162.7003	$162.70	$162.70	$162.70
7 purchase totals =	$1,277.55		$1,388.3425	$1,388.34	$1,388.30	$1,388.50