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	$107.69	4.754%	$112.8096	$112.81	$112.80	$112.80
Purchase #2	$56.49	9.610%	$61.9187	$61.92	$61.90	$61.90
Purchase #3	$133.47	12.402%	$150.0229	$150.02	$150.00	$150.00
Purchase #4	$196.35	3.353%	$202.9336	$202.93	$202.95	$202.90
Purchase #5	$93.81	7.109%	$100.479	$100.48	$100.50	$100.50
Purchase #6	$154.59	8.487%	$167.7101	$167.71	$167.70	$167.70
Purchase #7	$126.35	3.729%	$131.0616	$131.06	$131.05	$131.10
7 purchase totals =	$868.75		$926.9355	$926.93	$926.90	$926.90