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	$134.73	6.832%	$143.9348	$143.93	$143.95	$143.90
Purchase #2	$112.88	3.583%	$116.9245	$116.92	$116.90	$116.90
Purchase #3	$129.56	10.112%	$142.6611	$142.66	$142.65	$142.70
Purchase #4	$135.98	13.808%	$154.7561	$154.76	$154.75	$154.80
Purchase #5	$44.91	12.835%	$50.6742	$50.67	$50.65	$50.70
Purchase #6	$64.78	3.595%	$67.1088	$67.11	$67.10	$67.10
Purchase #7	$81.26	11.398%	$90.522	$90.52	$90.50	$90.50
7 purchase totals =	$704.10		$766.5815	$766.57	$766.50	$766.60