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	$112.89	13.202%	$127.7937	$127.79	$127.80	$127.80
Purchase #2	$21.27	13.564%	$24.1551	$24.16	$24.15	$24.20
Purchase #3	$197.67	12.597%	$222.5705	$222.57	$222.55	$222.60
Purchase #4	$80.55	11.553%	$89.8559	$89.86	$89.85	$89.90
Purchase #5	$50.78	9.119%	$55.4106	$55.41	$55.40	$55.40
Purchase #6	$124.59	5.314%	$131.2107	$131.21	$131.20	$131.20
Purchase #7	$182.90	8.581%	$198.5946	$198.59	$198.60	$198.60
7 purchase totals =	$770.65		$849.5911	$849.59	$849.55	$849.70