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	$99.76	13.186%	$112.9144	$112.91	$112.90	$112.90
Purchase #2	$225.78	12.646%	$254.3321	$254.33	$254.35	$254.30
Purchase #3	$63.59	13.539%	$72.1995	$72.20	$72.20	$72.20
Purchase #4	$85.60	6.233%	$90.9354	$90.94	$90.95	$90.90
Purchase #5	$64.68	9.845%	$71.0477	$71.05	$71.05	$71.00
Purchase #6	$87.36	13.390%	$99.0575	$99.06	$99.05	$99.10
Purchase #7	$127.55	7.373%	$136.9543	$136.95	$136.95	$137.00
7 purchase totals =	$754.32		$837.4409	$837.44	$837.45	$837.40