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	$121.94	4.401%	$127.3066	$127.31	$127.30	$127.30
Purchase #2	$94.79	9.228%	$103.5372	$103.54	$103.55	$103.50
Purchase #3	$56.59	12.303%	$63.5523	$63.55	$63.55	$63.60
Purchase #4	$139.44	9.503%	$152.691	$152.69	$152.70	$152.70
Purchase #5	$36.70	8.757%	$39.9138	$39.91	$39.90	$39.90
Purchase #6	$135.97	4.539%	$142.1417	$142.14	$142.15	$142.10
Purchase #7	$45.82	6.738%	$48.9074	$48.91	$48.90	$48.90
7 purchase totals =	$631.25		$678.0500	$678.05	$678.05	$678.00