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	$217.87	3.647%	$225.8157	$225.82	$225.80	$225.80
Purchase #2	$84.26	9.869%	$92.5756	$92.58	$92.60	$92.60
Purchase #3	$99.59	10.834%	$110.3796	$110.38	$110.40	$110.40
Purchase #4	$217.38	9.622%	$238.2963	$238.30	$238.30	$238.30
Purchase #5	$124.76	9.499%	$136.611	$136.61	$136.60	$136.60
Purchase #6	$176.94	6.768%	$188.9153	$188.92	$188.90	$188.90
Purchase #7	$80.53	10.416%	$88.918	$88.92	$88.90	$88.90
7 purchase totals =	$1,001.33		$1,081.5115	$1,081.53	$1,081.50	$1,081.50