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	$86.75	3.721%	$89.978	$89.98	$90.00	$90.00
Purchase #2	$209.49	5.674%	$221.3765	$221.38	$221.40	$221.40
Purchase #3	$196.49	13.400%	$222.8197	$222.82	$222.80	$222.80
Purchase #4	$109.25	6.637%	$116.5009	$116.50	$116.50	$116.50
Purchase #5	$17.44	13.653%	$19.8211	$19.82	$19.80	$19.80
Purchase #6	$41.49	7.833%	$44.7399	$44.74	$44.75	$44.70
Purchase #7	$166.80	6.767%	$178.0874	$178.09	$178.10	$178.10
7 purchase totals =	$827.71		$893.3235	$893.33	$893.35	$893.30