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	$137.44	6.365%	$146.1881	$146.19	$146.20	$146.20
Purchase #2	$47.48	11.402%	$52.8937	$52.89	$52.90	$52.90
Purchase #3	$9.31	12.522%	$10.4758	$10.48	$10.50	$10.50
Purchase #4	$136.65	4.288%	$142.5096	$142.51	$142.50	$142.50
Purchase #5	$162.82	4.502%	$170.1502	$170.15	$170.15	$170.20
Purchase #6	$84.50	4.516%	$88.316	$88.32	$88.30	$88.30
Purchase #7	$109.36	9.260%	$119.4867	$119.49	$119.50	$119.50
7 purchase totals =	$687.56		$730.0201	$730.03	$730.05	$730.10