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	$120.48	6.642%	$128.4823	$128.48	$128.50	$128.50
Purchase #2	$237.43	9.225%	$259.3329	$259.33	$259.35	$259.30
Purchase #3	$50.86	5.508%	$53.6614	$53.66	$53.65	$53.70
Purchase #4	$151.59	3.743%	$157.264	$157.26	$157.25	$157.30
Purchase #5	$59.75	8.204%	$64.6519	$64.65	$64.65	$64.70
Purchase #6	$63.51	12.715%	$71.5853	$71.59	$71.60	$71.60
Purchase #7	$193.54	3.506%	$200.3255	$200.33	$200.35	$200.30
7 purchase totals =	$877.16		$935.3033	$935.30	$935.35	$935.40