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	$151.26	10.462%	$167.0848	$167.08	$167.10	$167.10
Purchase #2	$140.91	7.382%	$151.312	$151.31	$151.30	$151.30
Purchase #3	$91.72	8.557%	$99.5685	$99.57	$99.55	$99.60
Purchase #4	$188.33	8.120%	$203.6224	$203.62	$203.60	$203.60
Purchase #5	$133.79	4.214%	$139.4279	$139.43	$139.45	$139.40
Purchase #6	$88.44	9.132%	$96.5163	$96.52	$96.50	$96.50
Purchase #7	$115.55	7.361%	$124.0556	$124.06	$124.05	$124.10
7 purchase totals =	$910.00		$981.5875	$981.59	$981.55	$981.60