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	$49.80	6.432%	$53.0031	$53.00	$53.00	$53.00
Purchase #2	$139.84	13.322%	$158.4695	$158.47	$158.45	$158.50
Purchase #3	$209.61	13.597%	$238.1107	$238.11	$238.10	$238.10
Purchase #4	$196.82	9.659%	$215.8308	$215.83	$215.85	$215.80
Purchase #5	$113.81	5.415%	$119.9728	$119.97	$119.95	$120.00
Purchase #6	$159.66	6.829%	$170.5632	$170.56	$170.55	$170.60
Purchase #7	$240.35	10.665%	$265.9833	$265.98	$266.00	$266.00
7 purchase totals =	$1,109.89		$1,221.9334	$1,221.92	$1,221.90	$1,222.00