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	$153.88	6.792%	$164.3315	$164.33	$164.35	$164.30
Purchase #2	$196.43	12.653%	$221.2843	$221.28	$221.30	$221.30
Purchase #3	$194.63	3.807%	$202.0396	$202.04	$202.05	$202.00
Purchase #4	$11.85	7.218%	$12.7053	$12.71	$12.70	$12.70
Purchase #5	$20.33	6.547%	$21.661	$21.66	$21.65	$21.70
Purchase #6	$175.82	7.500%	$189.0065	$189.01	$189.00	$189.00
Purchase #7	$91.38	13.241%	$103.4796	$103.48	$103.50	$103.50
7 purchase totals =	$844.32		$914.5078	$914.51	$914.55	$914.50