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	$40.79	11.317%	$45.4062	$45.41	$45.40	$45.40
Purchase #2	$53.39	12.110%	$59.8555	$59.86	$59.85	$59.90
Purchase #3	$15.84	9.611%	$17.3624	$17.36	$17.35	$17.40
Purchase #4	$100.37	5.564%	$105.9546	$105.95	$105.95	$106.00
Purchase #5	$86.96	6.818%	$92.8889	$92.89	$92.90	$92.90
Purchase #6	$68.80	7.393%	$73.8864	$73.89	$73.90	$73.90
Purchase #7	$25.59	11.417%	$28.5116	$28.51	$28.50	$28.50
7 purchase totals =	$391.74		$423.8656	$423.87	$423.85	$424.00