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	$155.94	6.566%	$166.179	$166.18	$166.20	$166.20
Purchase #2	$123.52	11.602%	$137.8508	$137.85	$137.85	$137.90
Purchase #3	$126.82	6.301%	$134.8109	$134.81	$134.80	$134.80
Purchase #4	$222.73	3.218%	$229.8975	$229.90	$229.90	$229.90
Purchase #5	$165.94	6.445%	$176.6348	$176.63	$176.65	$176.60
Purchase #6	$63.79	5.192%	$67.102	$67.10	$67.10	$67.10
Purchase #7	$86.91	4.756%	$91.0434	$91.04	$91.05	$91.00
7 purchase totals =	$945.65		$1,003.5184	$1,003.51	$1,003.55	$1,003.50