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	$41.68	3.280%	$43.0471	$43.05	$43.05	$43.00
Purchase #2	$204.74	9.320%	$223.8218	$223.82	$223.80	$223.80
Purchase #3	$43.72	4.713%	$45.7805	$45.78	$45.80	$45.80
Purchase #4	$140.34	4.700%	$146.936	$146.94	$146.95	$146.90
Purchase #5	$250.82	9.533%	$274.7307	$274.73	$274.75	$274.70
Purchase #6	$215.45	3.630%	$223.2708	$223.27	$223.25	$223.30
Purchase #7	$39.91	6.482%	$42.497	$42.50	$42.50	$42.50
7 purchase totals =	$936.66		$1,000.0839	$1,000.09	$1,000.10	$1,000.00