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	$129.86	9.589%	$142.3123	$142.31	$142.30	$142.30
Purchase #2	$235.42	8.340%	$255.054	$255.05	$255.05	$255.10
Purchase #3	$243.83	5.314%	$256.7871	$256.79	$256.80	$256.80
Purchase #4	$69.61	3.193%	$71.8326	$71.83	$71.85	$71.80
Purchase #5	$82.79	7.380%	$88.8999	$88.90	$88.90	$88.90
Purchase #6	$169.26	11.371%	$188.5066	$188.51	$188.50	$188.50
Purchase #7	$86.95	10.197%	$95.8163	$95.82	$95.80	$95.80
7 purchase totals =	$1,017.72		$1,099.2088	$1,099.21	$1,099.20	$1,099.20