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	$213.65	11.811%	$238.8842	$238.88	$238.90	$238.90
Purchase #2	$67.96	4.838%	$71.2479	$71.25	$71.25	$71.20
Purchase #3	$48.86	11.633%	$54.5439	$54.54	$54.55	$54.50
Purchase #4	$92.90	10.471%	$102.6276	$102.63	$102.65	$102.60
Purchase #5	$47.86	12.206%	$53.7018	$53.70	$53.70	$53.70
Purchase #6	$112.65	13.511%	$127.8701	$127.87	$127.85	$127.90
Purchase #7	$111.41	7.666%	$119.9507	$119.95	$119.95	$120.00
7 purchase totals =	$695.29		$768.8262	$768.82	$768.85	$768.80