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	$26.67	6.490%	$28.4009	$28.40	$28.40	$28.40
Purchase #2	$185.44	5.801%	$196.1974	$196.20	$196.20	$196.20
Purchase #3	$164.94	8.840%	$179.5207	$179.52	$179.50	$179.50
Purchase #4	$33.38	7.240%	$35.7967	$35.80	$35.80	$35.80
Purchase #5	$200.32	8.202%	$216.7502	$216.75	$216.75	$216.80
Purchase #6	$32.86	10.659%	$36.3625	$36.36	$36.35	$36.40
Purchase #7	$122.78	13.819%	$139.747	$139.75	$139.75	$139.70
7 purchase totals =	$766.39		$832.7754	$832.78	$832.75	$832.80