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	$102.73	9.856%	$112.8551	$112.86	$112.85	$112.90
Purchase #2	$62.72	3.446%	$64.8813	$64.88	$64.90	$64.90
Purchase #3	$182.90	8.535%	$198.5105	$198.51	$198.50	$198.50
Purchase #4	$152.42	5.128%	$160.2361	$160.24	$160.25	$160.20
Purchase #5	$150.70	6.164%	$159.9891	$159.99	$160.00	$160.00
Purchase #6	$65.68	9.531%	$71.94	$71.94	$71.95	$71.90
Purchase #7	$25.79	9.790%	$28.3148	$28.31	$28.30	$28.30
7 purchase totals =	$742.94		$796.7269	$796.73	$796.75	$796.70