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	$116.52	4.328%	$121.563	$121.56	$121.55	$121.60
Purchase #2	$234.52	3.800%	$243.4318	$243.43	$243.45	$243.40
Purchase #3	$170.46	8.801%	$185.4622	$185.46	$185.45	$185.50
Purchase #4	$18.34	11.774%	$20.4994	$20.50	$20.50	$20.50
Purchase #5	$63.96	3.713%	$66.3348	$66.33	$66.35	$66.30
Purchase #6	$87.62	3.392%	$90.5921	$90.59	$90.60	$90.60
Purchase #7	$117.98	7.388%	$126.6964	$126.70	$126.70	$126.70
7 purchase totals =	$809.40		$854.5797	$854.57	$854.60	$854.60