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	$94.33	3.160%	$97.3108	$97.31	$97.30	$97.30
Purchase #2	$128.53	9.132%	$140.2674	$140.27	$140.25	$140.30
Purchase #3	$101.87	10.830%	$112.9025	$112.90	$112.90	$112.90
Purchase #4	$218.78	5.867%	$231.6158	$231.62	$231.60	$231.60
Purchase #5	$180.65	9.846%	$198.4368	$198.44	$198.45	$198.40
Purchase #6	$137.75	7.388%	$147.927	$147.93	$147.95	$147.90
Purchase #7	$136.59	11.609%	$152.4467	$152.45	$152.45	$152.40
7 purchase totals =	$998.50		$1,080.9070	$1,080.92	$1,080.90	$1,080.80