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	$150.85	12.489%	$169.6897	$169.69	$169.70	$169.70
Purchase #2	$117.93	4.561%	$123.3088	$123.31	$123.30	$123.30
Purchase #3	$198.55	12.243%	$222.8585	$222.86	$222.85	$222.90
Purchase #4	$164.91	8.627%	$179.1368	$179.14	$179.15	$179.10
Purchase #5	$133.71	7.821%	$144.1675	$144.17	$144.15	$144.20
Purchase #6	$81.74	10.579%	$90.3873	$90.39	$90.40	$90.40
Purchase #7	$9.61	3.370%	$9.9339	$9.93	$9.95	$9.90
7 purchase totals =	$857.30		$939.4825	$939.49	$939.50	$939.50