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	$250.84	9.372%	$274.3487	$274.35	$274.35	$274.30
Purchase #2	$215.59	3.272%	$222.6441	$222.64	$222.65	$222.60
Purchase #3	$205.45	3.448%	$212.5339	$212.53	$212.55	$212.50
Purchase #4	$55.70	7.529%	$59.8937	$59.89	$59.90	$59.90
Purchase #5	$224.61	6.283%	$238.7222	$238.72	$238.70	$238.70
Purchase #6	$112.38	10.264%	$123.9147	$123.91	$123.90	$123.90
Purchase #7	$230.63	3.509%	$238.7228	$238.72	$238.70	$238.70
7 purchase totals =	$1,295.20		$1,370.7801	$1,370.76	$1,370.75	$1,370.60