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	$39.77	7.861%	$42.8963	$42.90	$42.90	$42.90
Purchase #2	$158.91	10.633%	$175.8069	$175.81	$175.80	$175.80
Purchase #3	$84.80	7.416%	$91.0888	$91.09	$91.10	$91.10
Purchase #4	$185.67	3.356%	$191.9011	$191.90	$191.90	$191.90
Purchase #5	$202.50	5.568%	$213.7752	$213.78	$213.80	$213.80
Purchase #6	$130.50	8.376%	$141.4307	$141.43	$141.45	$141.40
Purchase #7	$105.57	3.358%	$109.115	$109.12	$109.10	$109.10
7 purchase totals =	$907.72		$966.0140	$966.03	$966.05	$966.00