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	$51.76	9.821%	$56.8433	$56.84	$56.85	$56.80
Purchase #2	$242.74	9.368%	$265.4799	$265.48	$265.50	$265.50
Purchase #3	$59.87	9.789%	$65.7307	$65.73	$65.75	$65.70
Purchase #4	$230.61	4.368%	$240.683	$240.68	$240.70	$240.70
Purchase #5	$55.47	12.624%	$62.4725	$62.47	$62.45	$62.50
Purchase #6	$67.91	7.414%	$72.9448	$72.94	$72.95	$72.90
Purchase #7	$32.71	12.505%	$36.8004	$36.80	$36.80	$36.80
7 purchase totals =	$741.07		$800.9546	$800.94	$801.00	$800.90