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	$78.94	6.260%	$83.8816	$83.88	$83.90	$83.90
Purchase #2	$88.66	7.384%	$95.2067	$95.21	$95.20	$95.20
Purchase #3	$84.25	4.248%	$87.8289	$87.83	$87.85	$87.80
Purchase #4	$134.73	13.176%	$152.482	$152.48	$152.50	$152.50
Purchase #5	$130.86	4.560%	$136.8272	$136.83	$136.85	$136.80
Purchase #6	$62.71	3.355%	$64.8139	$64.81	$64.80	$64.80
Purchase #7	$64.40	10.654%	$71.2612	$71.26	$71.25	$71.30
7 purchase totals =	$644.55		$692.3015	$692.30	$692.35	$692.30