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	$126.63	12.303%	$142.2093	$142.21	$142.20	$142.20
Purchase #2	$61.33	8.473%	$66.5265	$66.53	$66.55	$66.50
Purchase #3	$55.32	13.480%	$62.7771	$62.78	$62.80	$62.80
Purchase #4	$115.50	11.438%	$128.7109	$128.71	$128.70	$128.70
Purchase #5	$156.37	3.341%	$161.5943	$161.59	$161.60	$161.60
Purchase #6	$152.25	9.375%	$166.5234	$166.52	$166.50	$166.50
Purchase #7	$92.31	9.315%	$100.9087	$100.91	$100.90	$100.90
7 purchase totals =	$759.71		$829.2502	$829.25	$829.25	$829.20