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	$127.90	7.471%	$137.4554	$137.46	$137.45	$137.50
Purchase #2	$83.78	9.276%	$91.5514	$91.55	$91.55	$91.60
Purchase #3	$58.39	5.668%	$61.6995	$61.70	$61.70	$61.70
Purchase #4	$134.89	3.435%	$139.5235	$139.52	$139.50	$139.50
Purchase #5	$150.40	9.473%	$164.6474	$164.65	$164.65	$164.60
Purchase #6	$166.38	8.485%	$180.4973	$180.50	$180.50	$180.50
Purchase #7	$196.46	4.273%	$204.8547	$204.85	$204.85	$204.90
7 purchase totals =	$918.20		$980.2292	$980.23	$980.20	$980.30