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	$76.92	4.605%	$80.4622	$80.46	$80.45	$80.50
Purchase #2	$109.95	6.859%	$117.4915	$117.49	$117.50	$117.50
Purchase #3	$212.97	11.736%	$237.9642	$237.96	$237.95	$238.00
Purchase #4	$89.61	4.155%	$93.3333	$93.33	$93.35	$93.30
Purchase #5	$81.90	9.354%	$89.5609	$89.56	$89.55	$89.60
Purchase #6	$206.35	13.197%	$233.582	$233.58	$233.60	$233.60
Purchase #7	$93.95	12.640%	$105.8253	$105.83	$105.85	$105.80
7 purchase totals =	$871.65		$958.2194	$958.21	$958.25	$958.30