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	$75.25	6.425%	$80.0848	$80.08	$80.10	$80.10
Purchase #2	$86.68	7.650%	$93.311	$93.31	$93.30	$93.30
Purchase #3	$79.60	12.546%	$89.5866	$89.59	$89.60	$89.60
Purchase #4	$240.66	9.467%	$263.4433	$263.44	$263.45	$263.40
Purchase #5	$51.64	4.540%	$53.9845	$53.98	$54.00	$54.00
Purchase #6	$135.77	5.118%	$142.7187	$142.72	$142.70	$142.70
Purchase #7	$144.38	13.654%	$164.0936	$164.09	$164.10	$164.10
7 purchase totals =	$813.98		$887.2225	$887.21	$887.25	$887.20