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	$20.50	8.573%	$22.2575	$22.26	$22.25	$22.30
Purchase #2	$24.63	10.493%	$27.2144	$27.21	$27.20	$27.20
Purchase #3	$147.71	3.446%	$152.8001	$152.80	$152.80	$152.80
Purchase #4	$80.93	10.142%	$89.1379	$89.14	$89.15	$89.10
Purchase #5	$59.59	4.299%	$62.1518	$62.15	$62.15	$62.20
Purchase #6	$76.43	12.304%	$85.8339	$85.83	$85.85	$85.80
Purchase #7	$91.76	7.849%	$98.9622	$98.96	$98.95	$99.00
7 purchase totals =	$501.55		$538.3578	$538.35	$538.35	$538.40