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	$20.53	6.768%	$21.9195	$21.92	$21.90	$21.90
Purchase #2	$82.26	6.863%	$87.9055	$87.91	$87.90	$87.90
Purchase #3	$41.53	8.348%	$44.9969	$45.00	$45.00	$45.00
Purchase #4	$49.79	6.802%	$53.1767	$53.18	$53.20	$53.20
Purchase #5	$31.25	7.359%	$33.5497	$33.55	$33.55	$33.50
Purchase #6	$28.52	9.259%	$31.1607	$31.16	$31.15	$31.20
Purchase #7	$238.78	10.841%	$264.6661	$264.67	$264.65	$264.70
7 purchase totals =	$492.66		$537.3751	$537.39	$537.35	$537.40