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	$75.89	12.605%	$85.4559	$85.46	$85.45	$85.50
Purchase #2	$84.43	5.845%	$89.3649	$89.36	$89.35	$89.40
Purchase #3	$150.65	12.494%	$169.4722	$169.47	$169.45	$169.50
Purchase #4	$41.45	5.511%	$43.7343	$43.73	$43.75	$43.70
Purchase #5	$51.47	7.106%	$55.1275	$55.13	$55.15	$55.10
Purchase #6	$222.96	6.836%	$238.2015	$238.20	$238.20	$238.20
Purchase #7	$127.98	9.449%	$140.0728	$140.07	$140.05	$140.10
7 purchase totals =	$754.83		$821.4291	$821.42	$821.40	$821.50