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	$77.44	12.108%	$86.8164	$86.82	$86.80	$86.80
Purchase #2	$139.66	4.343%	$145.7254	$145.73	$145.75	$145.70
Purchase #3	$37.87	9.700%	$41.5434	$41.54	$41.55	$41.50
Purchase #4	$167.97	3.295%	$173.5046	$173.50	$173.50	$173.50
Purchase #5	$234.66	13.277%	$265.8158	$265.82	$265.80	$265.80
Purchase #6	$81.69	12.482%	$91.8865	$91.89	$91.90	$91.90
Purchase #7	$147.55	13.823%	$167.9458	$167.95	$167.95	$167.90
7 purchase totals =	$886.84		$973.2379	$973.25	$973.25	$973.10