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	$158.59	10.679%	$175.5258	$175.53	$175.55	$175.50
Purchase #2	$128.38	11.303%	$142.8908	$142.89	$142.90	$142.90
Purchase #3	$84.86	3.238%	$87.6078	$87.61	$87.60	$87.60
Purchase #4	$61.29	10.116%	$67.4901	$67.49	$67.50	$67.50
Purchase #5	$53.90	11.711%	$60.2122	$60.21	$60.20	$60.20
Purchase #6	$116.80	6.658%	$124.5765	$124.58	$124.60	$124.60
Purchase #7	$164.37	9.673%	$180.2695	$180.27	$180.25	$180.30
7 purchase totals =	$768.19		$838.5727	$838.58	$838.60	$838.60