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	$55.57	4.641%	$58.149	$58.15	$58.15	$58.10
Purchase #2	$243.71	9.270%	$266.3019	$266.30	$266.30	$266.30
Purchase #3	$71.83	13.223%	$81.3281	$81.33	$81.35	$81.30
Purchase #4	$137.85	7.154%	$147.7118	$147.71	$147.70	$147.70
Purchase #5	$13.76	12.304%	$15.453	$15.45	$15.45	$15.50
Purchase #6	$14.56	6.438%	$15.4974	$15.50	$15.50	$15.50
Purchase #7	$86.66	4.532%	$90.5874	$90.59	$90.60	$90.60
7 purchase totals =	$623.94		$675.0286	$675.03	$675.05	$675.00