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	$21.72	6.461%	$23.1233	$23.12	$23.10	$23.10
Purchase #2	$21.40	6.629%	$22.8186	$22.82	$22.80	$22.80
Purchase #3	$73.90	11.310%	$82.2581	$82.26	$82.25	$82.30
Purchase #4	$86.62	3.666%	$89.7955	$89.80	$89.80	$89.80
Purchase #5	$156.28	5.448%	$164.7941	$164.79	$164.80	$164.80
Purchase #6	$155.94	12.460%	$175.3701	$175.37	$175.35	$175.40
Purchase #7	$162.40	10.743%	$179.8466	$179.85	$179.85	$179.80
7 purchase totals =	$678.26		$738.0063	$738.01	$737.95	$738.00