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	$172.81	12.397%	$194.2333	$194.23	$194.25	$194.20
Purchase #2	$142.33	12.748%	$160.4742	$160.47	$160.45	$160.50
Purchase #3	$202.63	3.323%	$209.3634	$209.36	$209.35	$209.40
Purchase #4	$16.77	9.660%	$18.39	$18.39	$18.40	$18.40
Purchase #5	$38.71	12.478%	$43.5402	$43.54	$43.55	$43.50
Purchase #6	$169.90	11.752%	$189.8666	$189.87	$189.85	$189.90
Purchase #7	$82.41	5.469%	$86.917	$86.92	$86.90	$86.90
7 purchase totals =	$825.56		$902.7847	$902.78	$902.75	$902.80