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	$247.74	12.560%	$278.8561	$278.86	$278.85	$278.90
Purchase #2	$59.37	12.669%	$66.8916	$66.89	$66.90	$66.90
Purchase #3	$65.51	6.804%	$69.9673	$69.97	$69.95	$70.00
Purchase #4	$158.91	8.752%	$172.8178	$172.82	$172.80	$172.80
Purchase #5	$86.57	10.599%	$95.7456	$95.75	$95.75	$95.70
Purchase #6	$108.46	13.699%	$123.3179	$123.32	$123.30	$123.30
Purchase #7	$79.69	8.288%	$86.2947	$86.29	$86.30	$86.30
7 purchase totals =	$806.25		$893.8910	$893.90	$893.85	$893.90