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	$240.59	10.648%	$266.208	$266.21	$266.20	$266.20
Purchase #2	$58.60	11.494%	$65.3355	$65.34	$65.35	$65.30
Purchase #3	$202.61	6.407%	$215.5912	$215.59	$215.60	$215.60
Purchase #4	$231.56	11.639%	$258.5113	$258.51	$258.50	$258.50
Purchase #5	$19.25	10.822%	$21.3332	$21.33	$21.35	$21.30
Purchase #6	$150.49	13.663%	$171.0514	$171.05	$171.05	$171.10
Purchase #7	$137.50	8.314%	$148.9318	$148.93	$148.95	$148.90
7 purchase totals =	$1,040.60		$1,146.9624	$1,146.96	$1,147.00	$1,146.90