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	$6.47	12.697%	$7.2915	$7.29	$7.30	$7.30
Purchase #2	$99.78	3.589%	$103.3611	$103.36	$103.35	$103.40
Purchase #3	$196.38	9.439%	$214.9163	$214.92	$214.90	$214.90
Purchase #4	$170.74	6.828%	$182.3981	$182.40	$182.40	$182.40
Purchase #5	$168.96	12.647%	$190.3284	$190.33	$190.35	$190.30
Purchase #6	$12.57	5.381%	$13.2464	$13.25	$13.25	$13.20
Purchase #7	$215.76	12.144%	$241.9619	$241.96	$241.95	$242.00
7 purchase totals =	$870.66		$953.5037	$953.51	$953.50	$953.50