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	$190.36	11.408%	$212.0763	$212.08	$212.10	$212.10
Purchase #2	$36.90	9.483%	$40.3992	$40.40	$40.40	$40.40
Purchase #3	$169.71	12.805%	$191.4414	$191.44	$191.45	$191.40
Purchase #4	$43.28	5.282%	$45.566	$45.57	$45.55	$45.60
Purchase #5	$89.93	4.296%	$93.7934	$93.79	$93.80	$93.80
Purchase #6	$29.51	13.850%	$33.5971	$33.60	$33.60	$33.60
Purchase #7	$19.44	12.272%	$21.8257	$21.83	$21.85	$21.80
7 purchase totals =	$579.13		$638.6991	$638.71	$638.75	$638.70