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	$84.66	6.486%	$90.151	$90.15	$90.15	$90.20
Purchase #2	$82.96	3.493%	$85.8578	$85.86	$85.85	$85.90
Purchase #3	$215.93	7.792%	$232.7553	$232.76	$232.75	$232.80
Purchase #4	$23.57	3.499%	$24.3947	$24.39	$24.40	$24.40
Purchase #5	$92.40	3.127%	$95.2893	$95.29	$95.30	$95.30
Purchase #6	$111.96	12.711%	$126.1912	$126.19	$126.20	$126.20
Purchase #7	$12.35	5.471%	$13.0257	$13.03	$13.05	$13.00
7 purchase totals =	$623.83		$667.6650	$667.67	$667.70	$667.80