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	$74.51	9.680%	$81.7226	$81.72	$81.70	$81.70
Purchase #2	$106.89	5.807%	$113.0971	$113.10	$113.10	$113.10
Purchase #3	$157.91	9.196%	$172.4314	$172.43	$172.45	$172.40
Purchase #4	$245.62	10.145%	$270.5381	$270.54	$270.55	$270.50
Purchase #5	$135.45	5.444%	$142.8239	$142.82	$142.80	$142.80
Purchase #6	$166.63	7.505%	$179.1356	$179.14	$179.15	$179.10
Purchase #7	$117.46	11.572%	$131.0525	$131.05	$131.05	$131.10
7 purchase totals =	$1,004.47		$1,090.8012	$1,090.80	$1,090.80	$1,090.70