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	$27.72	4.213%	$28.8878	$28.89	$28.90	$28.90
Purchase #2	$210.34	13.471%	$238.6749	$238.67	$238.65	$238.70
Purchase #3	$221.97	3.150%	$228.9621	$228.96	$228.95	$229.00
Purchase #4	$27.79	3.148%	$28.6648	$28.66	$28.65	$28.70
Purchase #5	$50.62	10.347%	$55.8577	$55.86	$55.85	$55.90
Purchase #6	$211.49	8.527%	$229.5238	$229.52	$229.50	$229.50
Purchase #7	$66.32	6.123%	$70.3808	$70.38	$70.40	$70.40
7 purchase totals =	$816.25		$880.9519	$880.94	$880.90	$881.10