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	$201.27	8.386%	$218.1485	$218.15	$218.15	$218.10
Purchase #2	$75.76	3.315%	$78.2714	$78.27	$78.25	$78.30
Purchase #3	$73.95	6.602%	$78.8322	$78.83	$78.85	$78.80
Purchase #4	$13.41	3.243%	$13.8449	$13.84	$13.85	$13.80
Purchase #5	$53.63	12.237%	$60.1927	$60.19	$60.20	$60.20
Purchase #6	$230.90	3.273%	$238.4574	$238.46	$238.45	$238.50
Purchase #7	$75.70	13.171%	$85.6704	$85.67	$85.65	$85.70
7 purchase totals =	$724.62		$773.4175	$773.41	$773.40	$773.40