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	$28.50	7.854%	$30.7384	$30.74	$30.75	$30.70
Purchase #2	$163.77	11.472%	$182.5577	$182.56	$182.55	$182.60
Purchase #3	$99.83	4.164%	$103.9869	$103.99	$104.00	$104.00
Purchase #4	$62.36	7.717%	$67.1723	$67.17	$67.15	$67.20
Purchase #5	$172.85	10.351%	$190.7417	$190.74	$190.75	$190.70
Purchase #6	$144.88	5.515%	$152.8701	$152.87	$152.85	$152.90
Purchase #7	$189.94	3.652%	$196.8766	$196.88	$196.90	$196.90
7 purchase totals =	$862.13		$924.9437	$924.95	$924.95	$925.00