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	$67.44	3.753%	$69.971	$69.97	$69.95	$70.00
Purchase #2	$40.67	5.618%	$42.9548	$42.95	$42.95	$43.00
Purchase #3	$67.60	6.185%	$71.7811	$71.78	$71.80	$71.80
Purchase #4	$160.83	13.653%	$182.7881	$182.79	$182.80	$182.80
Purchase #5	$26.87	7.765%	$28.9565	$28.96	$28.95	$29.00
Purchase #6	$78.86	6.377%	$83.8889	$83.89	$83.90	$83.90
Purchase #7	$100.54	12.779%	$113.388	$113.39	$113.40	$113.40
7 purchase totals =	$542.81		$593.7284	$593.73	$593.75	$593.90