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	$60.57	6.820%	$64.7009	$64.70	$64.70	$64.70
Purchase #2	$169.31	10.385%	$186.8928	$186.89	$186.90	$186.90
Purchase #3	$42.56	4.855%	$44.6263	$44.63	$44.65	$44.60
Purchase #4	$166.37	11.451%	$185.421	$185.42	$185.40	$185.40
Purchase #5	$80.98	4.126%	$84.3212	$84.32	$84.30	$84.30
Purchase #6	$127.67	12.209%	$143.2572	$143.26	$143.25	$143.30
Purchase #7	$209.59	6.840%	$223.926	$223.93	$223.95	$223.90
7 purchase totals =	$857.05		$933.1454	$933.15	$933.15	$933.10