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	$72.94	6.318%	$77.5483	$77.55	$77.55	$77.50
Purchase #2	$225.33	3.638%	$233.5275	$233.53	$233.55	$233.50
Purchase #3	$80.32	13.227%	$90.9439	$90.94	$90.95	$90.90
Purchase #4	$239.36	7.641%	$257.6495	$257.65	$257.65	$257.60
Purchase #5	$18.81	11.265%	$20.9289	$20.93	$20.95	$20.90
Purchase #6	$187.76	6.568%	$200.0921	$200.09	$200.10	$200.10
Purchase #7	$176.32	5.258%	$185.5909	$185.59	$185.60	$185.60
7 purchase totals =	$1,000.84		$1,066.2811	$1,066.28	$1,066.35	$1,066.10