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	$73.87	5.874%	$78.2091	$78.21	$78.20	$78.20
Purchase #2	$31.49	5.456%	$33.2081	$33.21	$33.20	$33.20
Purchase #3	$70.88	11.232%	$78.8412	$78.84	$78.85	$78.80
Purchase #4	$172.44	5.806%	$182.4519	$182.45	$182.45	$182.50
Purchase #5	$14.90	13.271%	$16.8774	$16.88	$16.90	$16.90
Purchase #6	$38.43	4.392%	$40.1178	$40.12	$40.10	$40.10
Purchase #7	$227.31	4.228%	$236.9207	$236.92	$236.90	$236.90
7 purchase totals =	$629.32		$666.6262	$666.63	$666.60	$666.60