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	$123.68	6.335%	$131.5151	$131.52	$131.50	$131.50
Purchase #2	$102.42	7.827%	$110.4364	$110.44	$110.45	$110.40
Purchase #3	$238.37	11.311%	$265.332	$265.33	$265.35	$265.30
Purchase #4	$141.35	3.300%	$146.0146	$146.01	$146.00	$146.00
Purchase #5	$78.69	5.356%	$82.9046	$82.90	$82.90	$82.90
Purchase #6	$6.55	6.193%	$6.9556	$6.96	$6.95	$7.00
Purchase #7	$56.79	7.810%	$61.2253	$61.23	$61.25	$61.20
7 purchase totals =	$747.85		$804.3836	$804.39	$804.40	$804.30