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	$109.78	6.310%	$116.7071	$116.71	$116.70	$116.70
Purchase #2	$191.57	4.562%	$200.3094	$200.31	$200.30	$200.30
Purchase #3	$48.81	9.558%	$53.4753	$53.48	$53.50	$53.50
Purchase #4	$207.71	9.351%	$227.133	$227.13	$227.15	$227.10
Purchase #5	$110.82	11.756%	$123.848	$123.85	$123.85	$123.80
Purchase #6	$215.67	4.512%	$225.401	$225.40	$225.40	$225.40
Purchase #7	$12.62	6.769%	$13.4742	$13.47	$13.45	$13.50
7 purchase totals =	$896.98		$960.3480	$960.35	$960.35	$960.30