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	$73.56	7.140%	$78.8122	$78.81	$78.80	$78.80
Purchase #2	$162.92	11.750%	$182.0631	$182.06	$182.05	$182.10
Purchase #3	$203.52	12.443%	$228.844	$228.84	$228.85	$228.80
Purchase #4	$204.32	10.713%	$226.2088	$226.21	$226.20	$226.20
Purchase #5	$239.87	9.192%	$261.9189	$261.92	$261.90	$261.90
Purchase #6	$38.39	8.170%	$41.5265	$41.53	$41.55	$41.50
Purchase #7	$121.42	8.320%	$131.5221	$131.52	$131.50	$131.50
7 purchase totals =	$1,044.00		$1,150.8956	$1,150.89	$1,150.85	$1,150.80