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	$91.30	10.188%	$100.6016	$100.60	$100.60	$100.60
Purchase #2	$214.36	13.560%	$243.4272	$243.43	$243.45	$243.40
Purchase #3	$122.57	12.194%	$137.5162	$137.52	$137.50	$137.50
Purchase #4	$187.78	6.648%	$200.2636	$200.26	$200.25	$200.30
Purchase #5	$126.34	7.612%	$135.957	$135.96	$135.95	$136.00
Purchase #6	$95.50	9.227%	$104.3118	$104.31	$104.30	$104.30
Purchase #7	$109.72	10.649%	$121.4041	$121.40	$121.40	$121.40
7 purchase totals =	$947.57		$1,043.4815	$1,043.48	$1,043.45	$1,043.50