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	$140.96	10.230%	$155.3802	$155.38	$155.40	$155.40
Purchase #2	$82.71	9.632%	$90.6766	$90.68	$90.70	$90.70
Purchase #3	$82.61	12.588%	$93.0089	$93.01	$93.00	$93.00
Purchase #4	$107.63	6.410%	$114.5291	$114.53	$114.55	$114.50
Purchase #5	$223.56	12.623%	$251.78	$251.78	$251.80	$251.80
Purchase #6	$18.45	13.561%	$20.952	$20.95	$20.95	$21.00
Purchase #7	$44.40	13.514%	$50.4002	$50.40	$50.40	$50.40
7 purchase totals =	$700.32		$776.7270	$776.73	$776.80	$776.80