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	$39.27	7.578%	$42.2459	$42.25	$42.25	$42.20
Purchase #2	$217.85	10.310%	$240.3103	$240.31	$240.30	$240.30
Purchase #3	$159.79	12.183%	$179.2572	$179.26	$179.25	$179.30
Purchase #4	$15.79	3.184%	$16.2928	$16.29	$16.30	$16.30
Purchase #5	$12.40	3.381%	$12.8192	$12.82	$12.80	$12.80
Purchase #6	$82.90	5.401%	$87.3774	$87.38	$87.40	$87.40
Purchase #7	$185.34	5.538%	$195.6041	$195.60	$195.60	$195.60
7 purchase totals =	$713.34		$773.9069	$773.91	$773.90	$773.90