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	$54.67	3.825%	$56.7611	$56.76	$56.75	$56.80
Purchase #2	$32.95	6.355%	$35.044	$35.04	$35.05	$35.00
Purchase #3	$13.62	10.262%	$15.0177	$15.02	$15.00	$15.00
Purchase #4	$62.74	3.155%	$64.7194	$64.72	$64.70	$64.70
Purchase #5	$238.82	13.589%	$271.2732	$271.27	$271.25	$271.30
Purchase #6	$68.64	13.774%	$78.0945	$78.09	$78.10	$78.10
Purchase #7	$134.95	7.731%	$145.383	$145.38	$145.40	$145.40
7 purchase totals =	$606.39		$666.2929	$666.28	$666.25	$666.30